| Message ID | 20210309175546.5877-2-osalvador@suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Allocate memmap from hotadded memory (per device) | expand |
This looks essentially good to me, except some parts in mhp_supports_memmap_on_memory() > > +bool mhp_supports_memmap_on_memory(unsigned long size) > +{ > + unsigned long pageblock_size = PFN_PHYS(pageblock_nr_pages); > + unsigned long remaining_mem = size - PMD_SIZE; This looks weird. I think what you want to test is that a) "nr_vmemmap_pages * sizeof(struct page)" spans complete PMDs (IOW, we won't map too much via the altmap when populating a PMD in the vmemmap) b) "remaining = size - nr_vmemmap_pages * sizeof(struct page)" spans complete pageblock. right? > + > + /* > + * Besides having CONFIG_MHP_MEMMAP_ON_MEMORY, we need a few more > + * assumptions to hold true: > + * - we are working on a single memory block granularity > + * - the size of struct page is multiple of PMD. That's not what you are checking. (and the way it is phrase, I don;t think it makes sense) > + * - the remaining memory after having used part of the range > + * for vmemmap pages is pageblock aligned. > + * > + * The reason for the struct page to be multiple of PMD is because > + * otherwise two sections would intersect a PMD. This would go against > + * memmap-on-memory premise, as memory would stay pinned until both > + * sections were removed. > + * > + * And the reason for the remaining memory to be pageblock aligned is > + * because mm core functions work on pageblock granularity in order to > + * change page's migratetype. > + */ > + return memmap_on_memory && > + size == memory_block_size_bytes() && > + IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) && > + !(PMD_SIZE % sizeof(struct page)) && > + remaining_mem && > + IS_ALIGNED(remaining_mem, pageblock_size); > +} > + I suggest a restructuring, compressing the information like: " Besides having arch support and the feature enabled at runtime, we need a few more assumptions to hold true: a) We span a single memory block: memory onlining/offlining happens in memory block granularity. We don't want the vmemmap of online memory blocks to reside on offline memory blocks. In the future, we might want to support variable-sized memory blocks to make the feature more versatile. b) The vmemmap pages span complete PMDs: We don't want vmemmap code to populate memory from the altmap for unrelated parts (i.e., other memory blocks). c) The vmemmap pages (and thereby the pages that will be exposed to the buddy) have to cover full pageblocks: memory onlining/offlining code requires applicable ranges to be page-aligned, for example, to set the migratetypes properly. " Do we have to special case / protect against the vmemmap optimization for hugetlb pages? Or is that already blocked somehow and I missed it?
On 15.03.21 11:22, Oscar Salvador wrote: > On Thu, Mar 11, 2021 at 08:06:53PM +0100, David Hildenbrand wrote: >> This looks essentially good to me, except some parts in >> mhp_supports_memmap_on_memory() >> >>> +bool mhp_supports_memmap_on_memory(unsigned long size) >>> +{ >>> + unsigned long pageblock_size = PFN_PHYS(pageblock_nr_pages); >>> + unsigned long remaining_mem = size - PMD_SIZE; > > Hi David, thanks for the review! > >> This looks weird. I think what you want to test is that >> >> >> a) "nr_vmemmap_pages * sizeof(struct page)" spans complete PMDs (IOW, we >> won't map too much via the altmap when populating a PMD in the vmemmap) >> >> b) "remaining = size - nr_vmemmap_pages * sizeof(struct page)" spans >> complete pageblock. > > We do not know the nr_vmemmap_pages at this point in time, although it is > easy to pre-compute. > > For every section we populate, we use PMD_SIZE. So, PMD_SIZE/PAGE_SIZE lays > the nr_vmemmap_pages that are used for populating a single section. I find that cross reference to vmemmap code a little hard to digest. I would have assume that we don't have to care about PMDs in this code here at all. The vmemmap population code should handle that. I think I already mentioned that somewhere, I think it should be like this: a) vmemmap code should *never* populate more memory than requested for a single memory section when we are populating from the altmap. If that cannot be guaranteed for PMDs, then we have to fallback to populating base pages. Populating PMDs from an altmap with sizeof(struct page) == 64 is highly dangerous. Assume we have sizeof(struct page) == 56. A 128 MiB section spans 32768 pages - we need 32768 * sizeof(struct page) space for the vmemmap. With 64k pages we *can* use exactly one PMD. With 56k pages we need 448 individual (full!) pages for the vmemmap. IOW, we don't care how vmemmap code will do the mapping. vmemmap code has to get it right. IMHO, asserting it in this code is wrong. b) In this code, we really should only care about what memory onlining/offlining code can or can't do. We really only care that 1) size == memory_block_size_bytes() 2) remaining_size 3) IS_ALIGNED(remaining_size, pageblock_size); I think a) is a logical consequence of b) for x86-64, whereby the pageblock size corresponds to PMD, so we might not have to care about a) right now. See below for my take. > > But let me explain the reasoning I use in the current code: > > I will enumarate the assumptions that must hold true in order to support the > feature together with their check: > > - We span a single memory block > > size == memory_block_size_bytes() > > - The vmemmap pages span a complete PMD and no more than a PMD. > > !(PMD_SIZE % sizeof(struct page)) > > - The vmemmap pages and the pages exposed to the buddy have to cover full > pageblocks > > remaining_mem = size - PMD_SIZE; > IS_ALIGNED(remaining_mem, pageblock_size) > > Although this check only covers the range without the vmemmap pages, one could > argue that since we use only a PMD_SIZE at a time, we know that PMD_SIZE is > pageblock aligned, so the vmemmap range is PMD_SIZE as well. > > Now, I see how this might be confusing and rather incomplete. > So I guess a better and more clear way to write it would be: > > bool mhp_supports_memmap_on_memory(unsigned long size) > { > unsigned long nr_vmemmap_pages = PMD_SIZE / PAGE_SIZE; > unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page); > unsigned long remaining_size = size - vmemmap_size; > > return memmap_on_memory && > IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) && > size == memory_block_size_bytes() && > !(PMD_SIZE % vmemmap_size) && > IS_ALIGNED(vmemmap_size, pageblock_size) && > remaining_size && > IS_ALIGNED(remaining_size, pageblock_size); > } > > Note that above check is only for a single section, but if assumptions hold true > for a single section, it will for many as well. Okay, please document the statement about single sections, that's important to understand what's happening. My take would be bool mhp_supports_memmap_on_memory(unsigned long size) { /* * Note: We calculate for a single memory section. The calculation * implicitly covers memory blocks that span multiple sections. */ unsigned long nr_vmemmap_pages = SECTION_SIZE / PAGE_SIZE; unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page); unsigned long remaining_size = size - vmemmap_size; /* * Note: vmemmap code has to make sure to not populate more memory * via the altmap than absolutely necessary for a single section. * This always holds when we allocate pageblock-sized chunks from * the altmap, as we require pageblock alignment here. * * TODO, other doc */ return memmap_on_memory && IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) && size == memory_block_size_bytes() && remaining_size && IS_ALIGNED(remaining_size, pageblock_size); } For arm64 with 64k base pages it might not hold and we might have to fix vmemmap code to not over-populate PMDs (512 MB). I did not have a loom at the code, though. > >> I suggest a restructuring, compressing the information like: >> >> " >> Besides having arch support and the feature enabled at runtime, we need a >> few more assumptions to hold true: >> >> a) We span a single memory block: memory onlining/offlining happens in >> memory block granularity. We don't want the vmemmap of online memory blocks >> to reside on offline memory blocks. In the future, we might want to support >> variable-sized memory blocks to make the feature more versatile. >> >> b) The vmemmap pages span complete PMDs: We don't want vmemmap code to >> populate memory from the altmap for unrelated parts (i.e., other memory >> blocks). >> >> c) The vmemmap pages (and thereby the pages that will be exposed to the >> buddy) have to cover full pageblocks: memory onlining/offlining code >> requires applicable ranges to be page-aligned, for example, to set the >> migratetypes properly. >> " > > I am fine with the above, I already added it, thanks. > >> Do we have to special case / protect against the vmemmap optimization for >> hugetlb pages? Or is that already blocked somehow and I missed it? > > Yes, hugetlb-vmemmap feature disables vmemmap on PMD population [1] > > [1] https://patchwork.kernel.org/project/linux-mm/patch/20210308102807.59745-7-songmuchun@bytedance.com/ Sorry, I might be missing something important. How does that make both features run mutually exclusive? hugetlb-vmemmap only instructs to populate base pages on !altmap. I assume if hugetlb-vmemmap code stumbles over a PMD it will skip optimization. But what if your machine does not have boot_cpu_has(X86_FEATURE_PSE) -- IOW, you always populate base pages? Either hugetlb-vmemmap code would have to identify that these pages come from an altmap (how? PageReserved() is also used for boot memory), or both features have to somehow run mutually exclusive.
On 16.03.21 17:46, David Hildenbrand wrote: > On 15.03.21 11:22, Oscar Salvador wrote: >> On Thu, Mar 11, 2021 at 08:06:53PM +0100, David Hildenbrand wrote: >>> This looks essentially good to me, except some parts in >>> mhp_supports_memmap_on_memory() >>> >>>> +bool mhp_supports_memmap_on_memory(unsigned long size) >>>> +{ >>>> + unsigned long pageblock_size = PFN_PHYS(pageblock_nr_pages); >>>> + unsigned long remaining_mem = size - PMD_SIZE; >> >> Hi David, thanks for the review! >> >>> This looks weird. I think what you want to test is that >>> >>> >>> a) "nr_vmemmap_pages * sizeof(struct page)" spans complete PMDs (IOW, we >>> won't map too much via the altmap when populating a PMD in the vmemmap) >>> >>> b) "remaining = size - nr_vmemmap_pages * sizeof(struct page)" spans >>> complete pageblock. >> >> We do not know the nr_vmemmap_pages at this point in time, although it is >> easy to pre-compute. >> >> For every section we populate, we use PMD_SIZE. So, PMD_SIZE/PAGE_SIZE lays >> the nr_vmemmap_pages that are used for populating a single section. > > I find that cross reference to vmemmap code a little hard to digest. > I would have assume that we don't have to care about PMDs in this > code here at all. The vmemmap population code should handle that. > > I think I already mentioned that somewhere, I think it should be like this: > > a) vmemmap code should *never* populate more memory than requested for > a single memory section when we are populating from the altmap. > If that cannot be guaranteed for PMDs, then we have to fallback > to populating base pages. Populating PMDs from an altmap with > sizeof(struct page) == 64 is highly dangerous. > > Assume we have sizeof(struct page) == 56. A 128 MiB section > spans 32768 pages - we need 32768 * sizeof(struct page) > space for the vmemmap. > > With 64k pages we *can* use exactly one PMD. With 56k pages > we need 448 individual (full!) pages for the vmemmap. > > IOW, we don't care how vmemmap code will do the mapping. > vmemmap code has to get it right. IMHO, asserting it in > this code is wrong. > > > b) In this code, we really should only care about what > memory onlining/offlining code can or can't do. > We really only care that > > 1) size == memory_block_size_bytes() > 2) remaining_size > 3) IS_ALIGNED(remaining_size, pageblock_size); > > > I think a) is a logical consequence of b) for x86-64, > whereby the pageblock size corresponds to PMD, so we > might not have to care about a) right now. > > See below for my take. > > >> >> But let me explain the reasoning I use in the current code: >> >> I will enumarate the assumptions that must hold true in order to support the >> feature together with their check: >> >> - We span a single memory block >> >> size == memory_block_size_bytes() >> >> - The vmemmap pages span a complete PMD and no more than a PMD. >> >> !(PMD_SIZE % sizeof(struct page)) >> >> - The vmemmap pages and the pages exposed to the buddy have to cover full >> pageblocks >> >> remaining_mem = size - PMD_SIZE; >> IS_ALIGNED(remaining_mem, pageblock_size) >> >> Although this check only covers the range without the vmemmap pages, one could >> argue that since we use only a PMD_SIZE at a time, we know that PMD_SIZE is >> pageblock aligned, so the vmemmap range is PMD_SIZE as well. >> >> Now, I see how this might be confusing and rather incomplete. >> So I guess a better and more clear way to write it would be: >> >> bool mhp_supports_memmap_on_memory(unsigned long size) >> { >> unsigned long nr_vmemmap_pages = PMD_SIZE / PAGE_SIZE; >> unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page); >> unsigned long remaining_size = size - vmemmap_size; >> >> return memmap_on_memory && >> IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) && >> size == memory_block_size_bytes() && >> !(PMD_SIZE % vmemmap_size) && >> IS_ALIGNED(vmemmap_size, pageblock_size) && >> remaining_size && >> IS_ALIGNED(remaining_size, pageblock_size); >> } >> >> Note that above check is only for a single section, but if assumptions hold true >> for a single section, it will for many as well. > > Okay, please document the statement about single sections, that's > important to understand what's happening. > > My take would be > > bool mhp_supports_memmap_on_memory(unsigned long size) > { > /* > * Note: We calculate for a single memory section. The calculation > * implicitly covers memory blocks that span multiple sections. > */ > unsigned long nr_vmemmap_pages = SECTION_SIZE / PAGE_SIZE; > unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page); > unsigned long remaining_size = size - vmemmap_size; > > /* > * Note: vmemmap code has to make sure to not populate more memory > * via the altmap than absolutely necessary for a single section. > * This always holds when we allocate pageblock-sized chunks from > * the altmap, as we require pageblock alignment here. > * > * TODO, other doc > */ > return memmap_on_memory && > IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) && > size == memory_block_size_bytes() && > remaining_size && > IS_ALIGNED(remaining_size, pageblock_size); Oh, I forgot, we can also drop the check for "remaining_size" in that code. If we ever have PAGE_SIZE == sizeof(struct page) we'll be in bigger trouble :D
On Tue, Mar 16, 2021 at 06:45:17PM +0100, David Hildenbrand wrote: > > I find that cross reference to vmemmap code a little hard to digest. > > I would have assume that we don't have to care about PMDs in this > > code here at all. The vmemmap population code should handle that. > > > > I think I already mentioned that somewhere, I think it should be like this: > > > > a) vmemmap code should *never* populate more memory than requested for > > a single memory section when we are populating from the altmap. > > If that cannot be guaranteed for PMDs, then we have to fallback > > to populating base pages. Populating PMDs from an altmap with > > sizeof(struct page) == 64 is highly dangerous. I guess you meant sizeof(struct page) != 64 But other usecases of using altmap (ZONE_DEVICE stuff) might not care whether they have sub-populated PMDs when populating sections from altmap? Current vmemmap code populates PMD with PMD_SIZE if empty, and with basepages if there are still holes. > > Assume we have sizeof(struct page) == 56. A 128 MiB section > > spans 32768 pages - we need 32768 * sizeof(struct page) > > space for the vmemmap. > > With 64k pages we *can* use exactly one PMD. With 56k pages > > we need 448 individual (full!) pages for the vmemmap. > > > > IOW, we don't care how vmemmap code will do the mapping. > > vmemmap code has to get it right. IMHO, asserting it in > > this code is wrong. > > > > > > b) In this code, we really should only care about what > > memory onlining/offlining code can or can't do. > > We really only care that > > > > 1) size == memory_block_size_bytes() > > 2) remaining_size > > 3) IS_ALIGNED(remaining_size, pageblock_size); I agree with the above, but see below: > > Okay, please document the statement about single sections, that's > > important to understand what's happening. > > > > My take would be > > > > bool mhp_supports_memmap_on_memory(unsigned long size) > > { > > /* > > * Note: We calculate for a single memory section. The calculation > > */ > > unsigned long nr_vmemmap_pages = SECTION_SIZE / PAGE_SIZE; > > unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page); > > unsigned long remaining_size = size - vmemmap_size; While it might be true that we need to back off from populating with altmap in case PMDs are not going to be fully populated because of the size of the struct page (I am not still not sure though as I said above, other usecases might not care at all), I would go __for now__ with placing vmemmap_size == PMD_SIZE in the check below as well. If the check comes true, we know that we fully populate PMDs when populating sections, so the feature can be used. Then I commit to have a look whether we need to back off in vmemmap-populating code in case altmap && !NOT_FULLY_POPULATED_PMDS. What do you think?
On 17.03.21 15:08, Oscar Salvador wrote: > On Tue, Mar 16, 2021 at 06:45:17PM +0100, David Hildenbrand wrote: >>> I find that cross reference to vmemmap code a little hard to digest. >>> I would have assume that we don't have to care about PMDs in this >>> code here at all. The vmemmap population code should handle that. >>> >>> I think I already mentioned that somewhere, I think it should be like this: >>> >>> a) vmemmap code should *never* populate more memory than requested for >>> a single memory section when we are populating from the altmap. >>> If that cannot be guaranteed for PMDs, then we have to fallback >>> to populating base pages. Populating PMDs from an altmap with >>> sizeof(struct page) == 64 is highly dangerous. > > I guess you meant sizeof(struct page) != 64 > Yes! > But other usecases of using altmap (ZONE_DEVICE stuff) might not care whether > they have sub-populated PMDs when populating sections from altmap? Just assume you have two ranges [ ZONE_DEVICE 0 ][ ZONE_DEVICE 1] If the vmemmap of ZONE_DEVICE 1 could be taken from the altmap of ZONE_DEVICE 0, we could be in trouble, as both parts can be removed/repurposed independently ... > > Current vmemmap code populates PMD with PMD_SIZE if empty, and with basepages > if there are still holes. > >>> Assume we have sizeof(struct page) == 56. A 128 MiB section >>> spans 32768 pages - we need 32768 * sizeof(struct page) >>> space for the vmemmap. >>> With 64k pages we *can* use exactly one PMD. With 56k pages >>> we need 448 individual (full!) pages for the vmemmap. >>> >>> IOW, we don't care how vmemmap code will do the mapping. >>> vmemmap code has to get it right. IMHO, asserting it in >>> this code is wrong. >>> >>> >>> b) In this code, we really should only care about what >>> memory onlining/offlining code can or can't do. >>> We really only care that >>> >>> 1) size == memory_block_size_bytes() >>> 2) remaining_size >>> 3) IS_ALIGNED(remaining_size, pageblock_size); > > I agree with the above, but see below: > >>> Okay, please document the statement about single sections, that's >>> important to understand what's happening. >>> >>> My take would be >>> >>> bool mhp_supports_memmap_on_memory(unsigned long size) >>> { >>> /* >>> * Note: We calculate for a single memory section. The calculation >>> */ >>> unsigned long nr_vmemmap_pages = SECTION_SIZE / PAGE_SIZE; >>> unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page); >>> unsigned long remaining_size = size - vmemmap_size; > > While it might be true that we need to back off from populating with altmap in > case PMDs are not going to be fully populated because of the size of the struct > page (I am not still not sure though as I said above, other usecases might not > care at all), I would go __for now__ with placing vmemmap_size == PMD_SIZE in > the check below as well. > > If the check comes true, we know that we fully populate PMDs when populating > sections, so the feature can be used. > > Then I commit to have a look whether we need to back off in vmemmap-populating > code in case altmap && !NOT_FULLY_POPULATED_PMDS. > > What do you think? If we check for IS_ALIGNED(nr_vmemmap_pages, PMD_SIZE), please add a proper TODO comment that this is most probably the wrong place to take care of this.
On Wed, Mar 17, 2021 at 03:35:41PM +0100, David Hildenbrand wrote: > Just assume you have two ranges > > [ ZONE_DEVICE 0 ][ ZONE_DEVICE 1] > > If the vmemmap of ZONE_DEVICE 1 could be taken from the altmap of > ZONE_DEVICE 0, we could be in trouble, as both parts can be > removed/repurposed independently ... I have to say my knowledge about ZONE_DEVICE and its intrinsencs tend to 0, that is why I thought it might not matter, but I agree that this is only asking for trouble. > If we check for > > IS_ALIGNED(nr_vmemmap_pages, PMD_SIZE), please add a proper TODO comment > that this is most probably the wrong place to take care of this. Sure, I will stuff the check in there and place a big TODO comment so we do not forget about addressing this issue the right way. I will prepare a v5 (hopefully the last one) and do some more testing before sending it out. Thanks David!
On Thu, Mar 18, 2021 at 09:27:48AM +0100, Oscar Salvador wrote: > > If we check for > > > > IS_ALIGNED(nr_vmemmap_pages, PMD_SIZE), please add a proper TODO comment > > that this is most probably the wrong place to take care of this. > > Sure, I will stuff the check in there and place a big TODO comment so we > do not forget about addressing this issue the right way. Ok, I realized something while working on v5. Here is what I have right now: bool mhp_supports_memmap_on_memory(unsigned long size) { /* * Note: We calculate for a single memory section. The calculation * implicitly covers memory blocks that span multiple sections. * * Not all archs define SECTION_SIZE, but MIN_MEMORY_BLOCK_SIZE always * equals SECTION_SIZE, so use that instead. */ unsigned long nr_vmemmap_pages = MIN_MEMORY_BLOCK_SIZE / PAGE_SIZE; unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page); unsigned long remaining_size = size - vmemmap_size; /* * Besides having arch support and the feature enabled at runtime, we * need a few more assumptions to hold true: * * a) We span a single memory block: memory onlining/offlinin;g happens * in memory block granularity. We don't want the vmemmap of online * memory blocks to reside on offline memory blocks. In the future, * we might want to support variable-sized memory blocks to make the * feature more versatile. * * b) The vmemmap pages span complete PMDs: We don't want vmemmap code * to populate memory from the altmap for unrelated parts (i.e., * other memory blocks) * * c) The vmemmap pages (and thereby the pages that will be exposed to * the buddy) have to cover full pageblocks: memory onlining/offlining * code requires applicable ranges to be page-aligned, for example, to * set the migratetypes properly. * * TODO: Although we have a check here to make sure that vmemmap pages * fully populate a PMD, it is not the right place to check for * this. A much better solution involves improving vmemmap code * to fallback to base pages when trying to populate vmemmap using * altmap as an alternative source of memory, and we do not exactly * populate a single PMD. */ return memmap_on_memory && IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) && size == memory_block_size_bytes() && remaining_size && IS_ALIGNED(remaining_size, pageblock_size) && IS_ALIGNED(vmemmap_size, PMD_SIZE); } Assume we are on x86_64 to simplify the case. Above, nr_vmemmap_pages would be 32768 and vmemmap_size 2MB (exactly a PMD). Now, although correct, this nr_vmemmap_pages does not match with the altmap->alloc. static void * __meminit altmap_alloc_block_buf(unsigned long size, struct altmap) { ... ... nr_pfns = size >> PAGE_SHIFT; //size is PMD_SIZE altmap->alloc += nr_pfns; } altmap->alloc will be 512, 512 * 4K pages = 2MB. Of course, the reason they do not match is because in one case, we are saying a) how many pfns we need to cover a PMD_SIZE, while in the other case we say b) how many pages we need to cover SECTION_SIZE Then b) multiply for page_size to get the current size of it. So, I have mixed feeling about this. Would it be more clear to just do: bool mhp_supports_memmap_on_memory(unsigned long size) { /* * Note: We calculate for a single memory section. The calculation * implicitly covers memory blocks that span multiple sections. */ unsigned long nr_vmemmap_pages = PMD_SIZE / PAGE_SIZE; unsigned long vmemmap_size = nr_vmemmap_pages * PAGE_SIZE; unsigned long remaining_size = size - vmemmap_size; ... ...
On 18.03.21 11:38, Oscar Salvador wrote: > On Thu, Mar 18, 2021 at 09:27:48AM +0100, Oscar Salvador wrote: >>> If we check for >>> >>> IS_ALIGNED(nr_vmemmap_pages, PMD_SIZE), please add a proper TODO comment >>> that this is most probably the wrong place to take care of this. >> >> Sure, I will stuff the check in there and place a big TODO comment so we >> do not forget about addressing this issue the right way. > > Ok, I realized something while working on v5. > > Here is what I have right now: > > bool mhp_supports_memmap_on_memory(unsigned long size) > { > /* > * Note: We calculate for a single memory section. The calculation > * implicitly covers memory blocks that span multiple sections. > * > * Not all archs define SECTION_SIZE, but MIN_MEMORY_BLOCK_SIZE always > * equals SECTION_SIZE, so use that instead. > */ > unsigned long nr_vmemmap_pages = MIN_MEMORY_BLOCK_SIZE / PAGE_SIZE; Even clearer would be just using "size / PAGE_SIZE" here. The you can even drop the comment. > unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page); > unsigned long remaining_size = size - vmemmap_size; > > /* > * Besides having arch support and the feature enabled at runtime, we > * need a few more assumptions to hold true: > * > * a) We span a single memory block: memory onlining/offlinin;g happens > * in memory block granularity. We don't want the vmemmap of online > * memory blocks to reside on offline memory blocks. In the future, > * we might want to support variable-sized memory blocks to make the > * feature more versatile. > * > * b) The vmemmap pages span complete PMDs: We don't want vmemmap code > * to populate memory from the altmap for unrelated parts (i.e., > * other memory blocks) > * > * c) The vmemmap pages (and thereby the pages that will be exposed to > * the buddy) have to cover full pageblocks: memory onlining/offlining > * code requires applicable ranges to be page-aligned, for example, to > * set the migratetypes properly. > * > * TODO: Although we have a check here to make sure that vmemmap pages > * fully populate a PMD, it is not the right place to check for > * this. A much better solution involves improving vmemmap code > * to fallback to base pages when trying to populate vmemmap using > * altmap as an alternative source of memory, and we do not exactly > * populate a single PMD. > */ > return memmap_on_memory && > IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) && > size == memory_block_size_bytes() && > remaining_size && > IS_ALIGNED(remaining_size, pageblock_size) && > IS_ALIGNED(vmemmap_size, PMD_SIZE); > } > > Assume we are on x86_64 to simplify the case. > > Above, nr_vmemmap_pages would be 32768 and vmemmap_size 2MB (exactly a > PMD). > > Now, although correct, this nr_vmemmap_pages does not match with the > altmap->alloc. > > static void * __meminit altmap_alloc_block_buf(unsigned long size, > struct altmap) > { > ... > ... > nr_pfns = size >> PAGE_SHIFT; //size is PMD_SIZE > altmap->alloc += nr_pfns; > } > > altmap->alloc will be 512, 512 * 4K pages = 2MB. > > Of course, the reason they do not match is because in one case, we are > saying a) how many pfns we need to cover a PMD_SIZE, while in the > other case we say b) how many pages we need to cover SECTION_SIZE > > Then b) multiply for page_size to get the current size of it. I don't follow. 2MB == 2MB. And if there would be difference then we would be in the problem I brought up: vmemmap code allocating too much via the altmap, which can be very bad because might be populating more vmemmap than we actually need. > > So, I have mixed feeling about this. > Would it be more clear to just do: > > bool mhp_supports_memmap_on_memory(unsigned long size) > { > /* > * Note: We calculate for a single memory section. The calculation > * implicitly covers memory blocks that span multiple sections. > */ Then this comment is wrong > unsigned long nr_vmemmap_pages = PMD_SIZE / PAGE_SIZE; And this stuff just gets confusing. nr_vmemmap_pages = 2MiB / 4 KiB = 512; > unsigned long vmemmap_size = nr_vmemmap_pages * PAGE_SIZE; vmemmap_size = 512 * 4KiB = 2 MiB. That calculation wasn't very useful (/ PAGE_SIZE * PAGE_SIZE)? > unsigned long remaining_size = size - vmemmap_size; And here we could get something like remaining_size = 2 GiB - 2 MiB ? Which does not make any sense. > ... > ... > >
On Thu, Mar 18, 2021 at 12:24:16PM +0100, David Hildenbrand wrote: > I don't follow. 2MB == 2MB. And if there would be difference then we would > be in the problem I brought up: vmemmap code allocating too much via the > altmap, which can be very bad because might be populating more vmemmap than > we actually need. Yes, I meant to say nr_vmemmap_pages won't match, or IOW, won't have the same meaning. The end result is the same. > vmemmap_size = 512 * 4KiB = 2 MiB. > > That calculation wasn't very useful (/ PAGE_SIZE * PAGE_SIZE)? Yeah, somewhat redundant. > > > unsigned long remaining_size = size - vmemmap_size; > > And here we could get something like > > remaining_size = 2 GiB - 2 MiB Yes, vmemmap_size would need to scale with nr_sections to be relative to size. Just wanted to bring it up, because somene might wonder "ok, why do we have altmap->nr_pfns = X, and here nr_vmemmap_pages is Y" It was an effort to make it consistent, although I see it would bring more confusion other than anything, so disregard.
On 18.03.21 13:03, Oscar Salvador wrote: > On Thu, Mar 18, 2021 at 12:24:16PM +0100, David Hildenbrand wrote: >> I don't follow. 2MB == 2MB. And if there would be difference then we would >> be in the problem I brought up: vmemmap code allocating too much via the >> altmap, which can be very bad because might be populating more vmemmap than >> we actually need. > > Yes, I meant to say nr_vmemmap_pages won't match, or IOW, won't have the > same meaning. > The end result is the same. > >> vmemmap_size = 512 * 4KiB = 2 MiB. >> >> That calculation wasn't very useful (/ PAGE_SIZE * PAGE_SIZE)? > > Yeah, somewhat redundant. > >> >>> unsigned long remaining_size = size - vmemmap_size; >> >> And here we could get something like >> >> remaining_size = 2 GiB - 2 MiB > > Yes, vmemmap_size would need to scale with nr_sections to be relative to > size. > > Just wanted to bring it up, because somene might wonder > "ok, why do we have altmap->nr_pfns = X, and here nr_vmemmap_pages > is Y" > > It was an effort to make it consistent, although I see it would bring > more confusion other than anything, so disregard. I am also unhappy that we have to replicate the same computation at two places, but I don't see an easy way to avoid that ... we have to trust on vmemmap code to do the right thing either way :(
diff --git a/drivers/base/memory.c b/drivers/base/memory.c index f35298425575..5ea2b3fbce02 100644 --- a/drivers/base/memory.c +++ b/drivers/base/memory.c @@ -175,7 +175,7 @@ int memory_notify(unsigned long val, void *v) */ static int memory_block_action(unsigned long start_section_nr, unsigned long action, - int online_type, int nid) + int online_type, int nid, unsigned long nr_vmemmap_pages) { unsigned long start_pfn; unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block; @@ -185,10 +185,11 @@ memory_block_action(unsigned long start_section_nr, unsigned long action, switch (action) { case MEM_ONLINE: - ret = online_pages(start_pfn, nr_pages, online_type, nid); + ret = online_pages(start_pfn, nr_pages, nr_vmemmap_pages, + online_type, nid); break; case MEM_OFFLINE: - ret = offline_pages(start_pfn, nr_pages); + ret = offline_pages(start_pfn, nr_pages, nr_vmemmap_pages); break; default: WARN(1, KERN_WARNING "%s(%ld, %ld) unknown action: " @@ -211,7 +212,7 @@ static int memory_block_change_state(struct memory_block *mem, mem->state = MEM_GOING_OFFLINE; ret = memory_block_action(mem->start_section_nr, to_state, - mem->online_type, mem->nid); + mem->online_type, mem->nid, mem->nr_vmemmap_pages); mem->state = ret ? from_state_req : to_state; @@ -567,7 +568,8 @@ int register_memory(struct memory_block *memory) return ret; } -static int init_memory_block(unsigned long block_id, unsigned long state) +static int init_memory_block(unsigned long block_id, unsigned long state, + unsigned long nr_vmemmap_pages) { struct memory_block *mem; int ret = 0; @@ -584,6 +586,7 @@ static int init_memory_block(unsigned long block_id, unsigned long state) mem->start_section_nr = block_id * sections_per_block; mem->state = state; mem->nid = NUMA_NO_NODE; + mem->nr_vmemmap_pages = nr_vmemmap_pages; ret = register_memory(mem); @@ -603,7 +606,7 @@ static int add_memory_block(unsigned long base_section_nr) if (section_count == 0) return 0; return init_memory_block(memory_block_id(base_section_nr), - MEM_ONLINE); + MEM_ONLINE, 0); } static void unregister_memory(struct memory_block *memory) @@ -625,7 +628,8 @@ static void unregister_memory(struct memory_block *memory) * * Called under device_hotplug_lock. */ -int create_memory_block_devices(unsigned long start, unsigned long size) +int create_memory_block_devices(unsigned long start, unsigned long size, + unsigned long vmemmap_pages) { const unsigned long start_block_id = pfn_to_block_id(PFN_DOWN(start)); unsigned long end_block_id = pfn_to_block_id(PFN_DOWN(start + size)); @@ -638,7 +642,7 @@ int create_memory_block_devices(unsigned long start, unsigned long size) return -EINVAL; for (block_id = start_block_id; block_id != end_block_id; block_id++) { - ret = init_memory_block(block_id, MEM_OFFLINE); + ret = init_memory_block(block_id, MEM_OFFLINE, vmemmap_pages); if (ret) break; } diff --git a/include/linux/memory.h b/include/linux/memory.h index 4da95e684e20..97e92e8b556a 100644 --- a/include/linux/memory.h +++ b/include/linux/memory.h @@ -29,6 +29,11 @@ struct memory_block { int online_type; /* for passing data to online routine */ int nid; /* NID for this memory block */ struct device dev; + /* + * Number of vmemmap pages. These pages + * lay at the beginning of the memory block. + */ + unsigned long nr_vmemmap_pages; }; int arch_get_memory_phys_device(unsigned long start_pfn); @@ -80,7 +85,8 @@ static inline int memory_notify(unsigned long val, void *v) #else extern int register_memory_notifier(struct notifier_block *nb); extern void unregister_memory_notifier(struct notifier_block *nb); -int create_memory_block_devices(unsigned long start, unsigned long size); +int create_memory_block_devices(unsigned long start, unsigned long size, + unsigned long vmemmap_pages); void remove_memory_block_devices(unsigned long start, unsigned long size); extern void memory_dev_init(void); extern int memory_notify(unsigned long val, void *v); diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h index 7288aa5ef73b..a85d4b7d15c2 100644 --- a/include/linux/memory_hotplug.h +++ b/include/linux/memory_hotplug.h @@ -55,6 +55,14 @@ typedef int __bitwise mhp_t; */ #define MHP_MERGE_RESOURCE ((__force mhp_t)BIT(0)) +/* + * We want memmap (struct page array) to be self contained. + * To do so, we will use the beginning of the hot-added range to build + * the page tables for the memmap array that describes the entire range. + * Only selected architectures support it with SPARSE_VMEMMAP. + */ +#define MHP_MEMMAP_ON_MEMORY ((__force mhp_t)BIT(1)) + /* * Extended parameters for memory hotplug: * altmap: alternative allocator for memmap array (optional) @@ -101,11 +109,13 @@ extern int zone_grow_waitqueues(struct zone *zone, unsigned long nr_pages); extern int add_one_highpage(struct page *page, int pfn, int bad_ppro); /* VM interface that may be used by firmware interface */ extern int online_pages(unsigned long pfn, unsigned long nr_pages, - int online_type, int nid); + unsigned long nr_vmemmap_pages, int online_type, + int nid); extern struct zone *test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn); extern void __offline_isolated_pages(unsigned long start_pfn, - unsigned long end_pfn); + unsigned long end_pfn, + unsigned long buddy_start_pfn); typedef void (*online_page_callback_t)(struct page *page, unsigned int order); @@ -307,7 +317,8 @@ static inline void pgdat_resize_init(struct pglist_data *pgdat) {} #ifdef CONFIG_MEMORY_HOTREMOVE extern void try_offline_node(int nid); -extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages); +extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages, + unsigned long nr_vmemmap_pages); extern int remove_memory(int nid, u64 start, u64 size); extern void __remove_memory(int nid, u64 start, u64 size); extern int offline_and_remove_memory(int nid, u64 start, u64 size); @@ -315,7 +326,8 @@ extern int offline_and_remove_memory(int nid, u64 start, u64 size); #else static inline void try_offline_node(int nid) {} -static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages) +static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages, + unsigned long nr_vmemmap_pages) { return -EINVAL; } @@ -359,6 +371,7 @@ extern struct zone *zone_for_pfn_range(int online_type, int nid, unsigned start_ extern int arch_create_linear_mapping(int nid, u64 start, u64 size, struct mhp_params *params); void arch_remove_linear_mapping(u64 start, u64 size); +extern bool mhp_supports_memmap_on_memory(unsigned long size); #endif /* CONFIG_MEMORY_HOTPLUG */ #endif /* __LINUX_MEMORY_HOTPLUG_H */ diff --git a/include/linux/memremap.h b/include/linux/memremap.h index f5b464daeeca..45a79da89c5f 100644 --- a/include/linux/memremap.h +++ b/include/linux/memremap.h @@ -17,7 +17,7 @@ struct device; * @alloc: track pages consumed, private to vmemmap_populate() */ struct vmem_altmap { - const unsigned long base_pfn; + unsigned long base_pfn; const unsigned long end_pfn; const unsigned long reserve; unsigned long free; diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 47946cec7584..747e1c21d8e2 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -427,6 +427,11 @@ enum zone_type { * techniques might use alloc_contig_range() to hide previously * exposed pages from the buddy again (e.g., to implement some sort * of memory unplug in virtio-mem). + * 6. Memory-hotplug: when using memmap_on_memory and onlining the memory + * to the MOVABLE zone, the vmemmap pages are also placed in such + * zone. Such pages cannot be really moved around as they are + * self-stored in the range, but they are treated as movable when + * the range they describe is about to be offlined. * * In general, no unmovable allocations that degrade memory offlining * should end up in ZONE_MOVABLE. Allocators (like alloc_contig_range()) diff --git a/mm/Kconfig b/mm/Kconfig index 24c045b24b95..febf805000f8 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -183,6 +183,11 @@ config MEMORY_HOTREMOVE depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE depends on MIGRATION +config MHP_MEMMAP_ON_MEMORY + def_bool y + depends on MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP + depends on ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE + # Heavily threaded applications may benefit from splitting the mm-wide # page_table_lock, so that faults on different parts of the user address # space can be handled with less contention: split it at this NR_CPUS. diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 5ba51a8bdaeb..63e5a0e9a6f3 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -42,6 +42,8 @@ #include "internal.h" #include "shuffle.h" +static bool memmap_on_memory; + /* * online_page_callback contains pointer to current page onlining function. * Initially it is generic_online_page(). If it is required it could be @@ -638,10 +640,22 @@ void generic_online_page(struct page *page, unsigned int order) } EXPORT_SYMBOL_GPL(generic_online_page); -static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages) +static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages, + unsigned long buddy_start_pfn) { const unsigned long end_pfn = start_pfn + nr_pages; - unsigned long pfn; + unsigned long pfn = buddy_start_pfn; + + /* + * When using memmap_on_memory, the range might be unaligned as the + * first pfns are used for vmemmap pages. Align it in case we need to. + */ + VM_BUG_ON(!IS_ALIGNED(pfn, pageblock_nr_pages)); + + while (!IS_ALIGNED(pfn, MAX_ORDER_NR_PAGES)) { + (*online_page_callback)(pfn_to_page(pfn), pageblock_order); + pfn += pageblock_nr_pages; + } /* * Online the pages in MAX_ORDER - 1 aligned chunks. The callback might @@ -649,7 +663,7 @@ static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages) * later). We account all pages as being online and belonging to this * zone ("present"). */ - for (pfn = start_pfn; pfn < end_pfn; pfn += MAX_ORDER_NR_PAGES) + for (; pfn < end_pfn; pfn += MAX_ORDER_NR_PAGES) (*online_page_callback)(pfn_to_page(pfn), MAX_ORDER - 1); /* mark all involved sections as online */ @@ -830,9 +844,9 @@ struct zone * zone_for_pfn_range(int online_type, int nid, unsigned start_pfn, } int __ref online_pages(unsigned long pfn, unsigned long nr_pages, - int online_type, int nid) + unsigned long nr_vmemmap_pages, int online_type, int nid) { - unsigned long flags; + unsigned long flags, buddy_start_pfn, buddy_nr_pages; struct zone *zone; int need_zonelists_rebuild = 0; int ret; @@ -843,11 +857,18 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION))) return -EINVAL; + buddy_start_pfn = pfn + nr_vmemmap_pages; + buddy_nr_pages = nr_pages - nr_vmemmap_pages; + mem_hotplug_begin(); /* associate pfn range with the zone */ zone = zone_for_pfn_range(online_type, nid, pfn, nr_pages); - move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_ISOLATE); + if (nr_vmemmap_pages) + move_pfn_range_to_zone(zone, pfn, nr_vmemmap_pages, NULL, + MIGRATE_UNMOVABLE); + move_pfn_range_to_zone(zone, buddy_start_pfn, buddy_nr_pages, NULL, + MIGRATE_ISOLATE); arg.start_pfn = pfn; arg.nr_pages = nr_pages; @@ -863,7 +884,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, * onlining, such that undo_isolate_page_range() works correctly. */ spin_lock_irqsave(&zone->lock, flags); - zone->nr_isolate_pageblock += nr_pages / pageblock_nr_pages; + zone->nr_isolate_pageblock += buddy_nr_pages / pageblock_nr_pages; spin_unlock_irqrestore(&zone->lock, flags); /* @@ -876,7 +897,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, setup_zone_pageset(zone); } - online_pages_range(pfn, nr_pages); + online_pages_range(pfn, nr_pages, buddy_start_pfn); zone->present_pages += nr_pages; pgdat_resize_lock(zone->zone_pgdat, &flags); @@ -889,7 +910,9 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, zone_pcp_update(zone); /* Basic onlining is complete, allow allocation of onlined pages. */ - undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE); + undo_isolate_page_range(buddy_start_pfn, + buddy_start_pfn + buddy_nr_pages, + MIGRATE_MOVABLE); /* * Freshly onlined pages aren't shuffled (e.g., all pages are placed to @@ -1064,6 +1087,36 @@ static int online_memory_block(struct memory_block *mem, void *arg) return device_online(&mem->dev); } +bool mhp_supports_memmap_on_memory(unsigned long size) +{ + unsigned long pageblock_size = PFN_PHYS(pageblock_nr_pages); + unsigned long remaining_mem = size - PMD_SIZE; + + /* + * Besides having CONFIG_MHP_MEMMAP_ON_MEMORY, we need a few more + * assumptions to hold true: + * - we are working on a single memory block granularity + * - the size of struct page is multiple of PMD. + * - the remaining memory after having used part of the range + * for vmemmap pages is pageblock aligned. + * + * The reason for the struct page to be multiple of PMD is because + * otherwise two sections would intersect a PMD. This would go against + * memmap-on-memory premise, as memory would stay pinned until both + * sections were removed. + * + * And the reason for the remaining memory to be pageblock aligned is + * because mm core functions work on pageblock granularity in order to + * change page's migratetype. + */ + return memmap_on_memory && + size == memory_block_size_bytes() && + IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) && + !(PMD_SIZE % sizeof(struct page)) && + remaining_mem && + IS_ALIGNED(remaining_mem, pageblock_size); +} + /* * NOTE: The caller must call lock_device_hotplug() to serialize hotplug * and online/offline operations (triggered e.g. by sysfs). @@ -1073,6 +1126,7 @@ static int online_memory_block(struct memory_block *mem, void *arg) int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags) { struct mhp_params params = { .pgprot = PAGE_KERNEL }; + struct vmem_altmap mhp_altmap = {}; u64 start, size; bool new_node = false; int ret; @@ -1099,13 +1153,26 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags) goto error; new_node = ret; + /* + * Self hosted memmap array + */ + if (mhp_flags & MHP_MEMMAP_ON_MEMORY) { + if (!mhp_supports_memmap_on_memory(size)) { + ret = -EINVAL; + goto error; + } + mhp_altmap.free = PHYS_PFN(size); + mhp_altmap.base_pfn = PHYS_PFN(start); + params.altmap = &mhp_altmap; + } + /* call arch's memory hotadd */ ret = arch_add_memory(nid, start, size, ¶ms); if (ret < 0) goto error; /* create memory block devices after memory was added */ - ret = create_memory_block_devices(start, size); + ret = create_memory_block_devices(start, size, mhp_altmap.alloc); if (ret) { arch_remove_memory(nid, start, size, NULL); goto error; @@ -1563,10 +1630,11 @@ static int count_system_ram_pages_cb(unsigned long start_pfn, return 0; } -int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages) +int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages, + unsigned long nr_vmemmap_pages) { const unsigned long end_pfn = start_pfn + nr_pages; - unsigned long pfn, system_ram_pages = 0; + unsigned long pfn, buddy_start_pfn, buddy_nr_pages, system_ram_pages = 0; unsigned long flags; struct zone *zone; struct memory_notify arg; @@ -1578,6 +1646,9 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages) !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION))) return -EINVAL; + buddy_start_pfn = start_pfn + nr_vmemmap_pages; + buddy_nr_pages = nr_pages - nr_vmemmap_pages; + mem_hotplug_begin(); /* @@ -1613,7 +1684,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages) zone_pcp_disable(zone); /* set above range as isolated */ - ret = start_isolate_page_range(start_pfn, end_pfn, + ret = start_isolate_page_range(buddy_start_pfn, end_pfn, MIGRATE_MOVABLE, MEMORY_OFFLINE | REPORT_FAILURE); if (ret) { @@ -1633,7 +1704,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages) } do { - pfn = start_pfn; + pfn = buddy_start_pfn; do { if (signal_pending(current)) { ret = -EINTR; @@ -1664,18 +1735,18 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages) * offlining actually in order to make hugetlbfs's object * counting consistent. */ - ret = dissolve_free_huge_pages(start_pfn, end_pfn); + ret = dissolve_free_huge_pages(buddy_start_pfn, end_pfn); if (ret) { reason = "failure to dissolve huge pages"; goto failed_removal_isolated; } - ret = test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE); + ret = test_pages_isolated(buddy_start_pfn, end_pfn, MEMORY_OFFLINE); } while (ret); /* Mark all sections offline and remove free pages from the buddy. */ - __offline_isolated_pages(start_pfn, end_pfn); + __offline_isolated_pages(start_pfn, end_pfn, buddy_start_pfn); pr_debug("Offlined Pages %ld\n", nr_pages); /* @@ -1684,13 +1755,13 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages) * of isolated pageblocks, memory onlining will properly revert this. */ spin_lock_irqsave(&zone->lock, flags); - zone->nr_isolate_pageblock -= nr_pages / pageblock_nr_pages; + zone->nr_isolate_pageblock -= buddy_nr_pages / pageblock_nr_pages; spin_unlock_irqrestore(&zone->lock, flags); zone_pcp_enable(zone); /* removal success */ - adjust_managed_page_count(pfn_to_page(start_pfn), -nr_pages); + adjust_managed_page_count(pfn_to_page(start_pfn), -buddy_nr_pages); zone->present_pages -= nr_pages; pgdat_resize_lock(zone->zone_pgdat, &flags); @@ -1719,7 +1790,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages) return 0; failed_removal_isolated: - undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE); + undo_isolate_page_range(buddy_start_pfn, end_pfn, MIGRATE_MOVABLE); memory_notify(MEM_CANCEL_OFFLINE, &arg); failed_removal_pcplists_disabled: zone_pcp_enable(zone); @@ -1750,6 +1821,14 @@ static int check_memblock_offlined_cb(struct memory_block *mem, void *arg) return 0; } +static int get_nr_vmemmap_pages_cb(struct memory_block *mem, void *arg) +{ + /* + * If not set, continue with the next block. + */ + return mem->nr_vmemmap_pages; +} + static int check_cpu_on_node(pg_data_t *pgdat) { int cpu; @@ -1824,6 +1903,9 @@ EXPORT_SYMBOL(try_offline_node); static int __ref try_remove_memory(int nid, u64 start, u64 size) { int rc = 0; + struct vmem_altmap mhp_altmap = {}; + struct vmem_altmap *altmap = NULL; + unsigned long nr_vmemmap_pages = 0; BUG_ON(check_hotplug_memory_range(start, size)); @@ -1836,6 +1918,31 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size) if (rc) return rc; + /* + * We only support removing memory added with MHP_MEMMAP_ON_MEMORY in + * the same granularity it was added - a single memory block. + */ + if (memmap_on_memory) { + nr_vmemmap_pages = walk_memory_blocks(start, size, NULL, + get_nr_vmemmap_pages_cb); + if (nr_vmemmap_pages) { + if (size != memory_block_size_bytes()) { + pr_warn("Refuse to remove %#llx - %#llx," + "wrong granularity\n", + start, start + size); + return -EINVAL; + } + + /* + * Let remove_pmd_table->free_hugepage_table + * do the right thing if we used vmem_altmap + * when hot-adding the range. + */ + mhp_altmap.alloc = nr_vmemmap_pages; + altmap = &mhp_altmap; + } + } + /* remove memmap entry */ firmware_map_remove(start, start + size, "System RAM"); @@ -1847,7 +1954,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size) mem_hotplug_begin(); - arch_remove_memory(nid, start, size, NULL); + arch_remove_memory(nid, start, size, altmap); if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) { memblock_free(start, size); diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3e4b29ee2b1e..85c478e374d7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8830,7 +8830,8 @@ void zone_pcp_reset(struct zone *zone) * All pages in the range must be in a single zone, must not contain holes, * must span full sections, and must be isolated before calling this function. */ -void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) +void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn, + unsigned long buddy_start_pfn) { unsigned long pfn = start_pfn; struct page *page; @@ -8841,6 +8842,7 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) offline_mem_sections(pfn, end_pfn); zone = page_zone(pfn_to_page(pfn)); spin_lock_irqsave(&zone->lock, flags); + pfn = buddy_start_pfn; while (pfn < end_pfn) { page = pfn_to_page(pfn); /*
Physical memory hotadd has to allocate a memmap (struct page array) for the newly added memory section. Currently, alloc_pages_node() is used for those allocations. This has some disadvantages: a) an existing memory is consumed for that purpose (eg: ~2MB per 128MB memory section on x86_64) b) if the whole node is movable then we have off-node struct pages which has performance drawbacks. c) It might be there are no PMD_ALIGNED chunks so memmap array gets populated with base pages. This can be improved when CONFIG_SPARSEMEM_VMEMMAP is enabled. Vmemap page tables can map arbitrary memory. That means that we can simply use the beginning of each memory section and map struct pages there. struct pages which back the allocated space then just need to be treated carefully. Implementation wise we will reuse vmem_altmap infrastructure to override the default allocator used by __populate_section_memmap. Part of the implementation also relies on memory_block structure gaining a new field which specifies the number of vmemmap_pages at the beginning. This comes in handy as in {online,offline}_pages, all the isolation and migration is being done on (buddy_start_pfn, end_pfn] range, being buddy_start_pfn = start_pfn + nr_vmemmap_pages. In this way, we have: [start_pfn, buddy_start_pfn - 1] = Initialized and PageReserved [buddy_start_pfn, end_pfn - 1] = Initialized and sent to buddy Hot-remove: We need to be careful when removing memory, as adding and removing memory needs to be done with the same granularity. To check that this assumption is not violated, we check the memory range we want to remove and if a) any memory block has vmemmap pages and b) the range spans more than a single memory block, we scream out loud and refuse to proceed. If all is good and the range was using memmap on memory (aka vmemmap pages), we construct an altmap structure so free_hugepage_table does the right thing and calls vmem_altmap_free instead of free_pagetable. Signed-off-by: Oscar Salvador <osalvador@suse.de> --- drivers/base/memory.c | 20 +++--- include/linux/memory.h | 8 ++- include/linux/memory_hotplug.h | 21 ++++-- include/linux/memremap.h | 2 +- include/linux/mmzone.h | 5 ++ mm/Kconfig | 5 ++ mm/memory_hotplug.c | 149 +++++++++++++++++++++++++++++++++++------ mm/page_alloc.c | 4 +- 8 files changed, 178 insertions(+), 36 deletions(-)