| Message ID | 20240708112445.2690631-1-ryan.roberts@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v1] mm: shmem: Rename mTHP shmem counters | expand |
On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts <ryan.roberts@arm.com> wrote: > > The legacy PMD-sized THP counters at /proc/vmstat include > thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which > rather confusingly refer to shmem THP and do not include any other types > of file pages. This is inconsistent since in most other places in the > kernel, THP counters are explicitly separated for anon, shmem and file > flavours. However, we are stuck with it since it constitutes a user ABI. > > Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for > anonymous shmem") added equivalent mTHP stats for shmem, keeping the > same "file_" prefix in the names. But in future, we may want to add > extra stats to cover actual file pages, at which point, it would all > become very confusing. > > So let's take the opportunity to rename these new counters "shmem_" > before the change makes it upstream and the ABI becomes immutable. Personally, I think this approach is much clearer. However, I recall we discussed this before [1], and it seems that inconsistency is a concern? [1] https://lore.kernel.org/linux-mm/05d0096e4ec3e572d1d52d33a31a661321ac1551.1713755580.git.baolin.wang@linux.alibaba.com/ > > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> > --- > > Hi All, > > Applies on top of today's mm-unstable (2073cda629a4) and tested with mm > selftests; no regressions observed. > > The backstory here is that I'd like to introduce some counters for regular file > folio allocations to observe how often large folio allocation succeeds, but > these shmem counters are named "file" which is going to make things confusing. > So hoping to solve that before commit 66f44583f9b6 ("mm: shmem: add mTHP > counters for anonymous shmem") goes upstream (it is currently in mm-stable). > > Admittedly, this change means the mTHP stat names are not the same as the legacy > PMD-size THP names, but I think that's a smaller issue than having "file_" mTHP > stats that only count shmem, then having to introduce "file2_" or "pgcache_" > stats for the regular file memory, which is even more inconsistent IMHO. I guess > the alternative is to count both shmem and file in these mTHP stats (that's how > they were documented anyway) but I think it's better to be able to consider them > separately like we do for all the other counters. > > Thanks, > Ryan > > Documentation/admin-guide/mm/transhuge.rst | 12 ++++++------ > include/linux/huge_mm.h | 6 +++--- > mm/huge_memory.c | 12 ++++++------ > mm/shmem.c | 8 ++++---- > 4 files changed, 19 insertions(+), 19 deletions(-) > > diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst > index 747c811ee8f1..8b891689fc13 100644 > --- a/Documentation/admin-guide/mm/transhuge.rst > +++ b/Documentation/admin-guide/mm/transhuge.rst > @@ -496,16 +496,16 @@ swpout_fallback > Usually because failed to allocate some continuous swap space > for the huge page. > > -file_alloc > - is incremented every time a file huge page is successfully > +shmem_alloc > + is incremented every time a shmem huge page is successfully > allocated. > > -file_fallback > - is incremented if a file huge page is attempted to be allocated > +shmem_fallback > + is incremented if a shmem huge page is attempted to be allocated > but fails and instead falls back to using small pages. > > -file_fallback_charge > - is incremented if a file huge page cannot be charged and instead > +shmem_fallback_charge > + is incremented if a shmem huge page cannot be charged and instead > falls back to using small pages even though the allocation was > successful. > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index acb6ac24a07e..cff002be83eb 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -269,9 +269,9 @@ enum mthp_stat_item { > MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE, > MTHP_STAT_SWPOUT, > MTHP_STAT_SWPOUT_FALLBACK, > - MTHP_STAT_FILE_ALLOC, > - MTHP_STAT_FILE_FALLBACK, > - MTHP_STAT_FILE_FALLBACK_CHARGE, > + MTHP_STAT_SHMEM_ALLOC, > + MTHP_STAT_SHMEM_FALLBACK, > + MTHP_STAT_SHMEM_FALLBACK_CHARGE, > MTHP_STAT_SPLIT, > MTHP_STAT_SPLIT_FAILED, > MTHP_STAT_SPLIT_DEFERRED, > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 9ec64aa2be94..f9696c94e211 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -568,9 +568,9 @@ DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK); > DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE); > DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT); > DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK); > -DEFINE_MTHP_STAT_ATTR(file_alloc, MTHP_STAT_FILE_ALLOC); > -DEFINE_MTHP_STAT_ATTR(file_fallback, MTHP_STAT_FILE_FALLBACK); > -DEFINE_MTHP_STAT_ATTR(file_fallback_charge, MTHP_STAT_FILE_FALLBACK_CHARGE); > +DEFINE_MTHP_STAT_ATTR(shmem_alloc, MTHP_STAT_SHMEM_ALLOC); > +DEFINE_MTHP_STAT_ATTR(shmem_fallback, MTHP_STAT_SHMEM_FALLBACK); > +DEFINE_MTHP_STAT_ATTR(shmem_fallback_charge, MTHP_STAT_SHMEM_FALLBACK_CHARGE); > DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT); > DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED); > DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED); > @@ -581,9 +581,9 @@ static struct attribute *stats_attrs[] = { > &anon_fault_fallback_charge_attr.attr, > &swpout_attr.attr, > &swpout_fallback_attr.attr, > - &file_alloc_attr.attr, > - &file_fallback_attr.attr, > - &file_fallback_charge_attr.attr, > + &shmem_alloc_attr.attr, > + &shmem_fallback_attr.attr, > + &shmem_fallback_charge_attr.attr, > &split_attr.attr, > &split_failed_attr.attr, > &split_deferred_attr.attr, > diff --git a/mm/shmem.c b/mm/shmem.c > index 921d59c3d669..f24dfbd387ba 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1777,7 +1777,7 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, > if (pages == HPAGE_PMD_NR) > count_vm_event(THP_FILE_FALLBACK); > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > - count_mthp_stat(order, MTHP_STAT_FILE_FALLBACK); > + count_mthp_stat(order, MTHP_STAT_SHMEM_FALLBACK); > #endif > order = next_order(&suitable_orders, order); > } > @@ -1804,8 +1804,8 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, > count_vm_event(THP_FILE_FALLBACK_CHARGE); > } > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK); > - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK_CHARGE); > + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK); > + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK_CHARGE); > #endif > } > goto unlock; > @@ -2181,7 +2181,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index, > if (folio_test_pmd_mappable(folio)) > count_vm_event(THP_FILE_ALLOC); > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_ALLOC); > + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_ALLOC); > #endif > goto alloced; > } > -- > 2.43.0 > Thanks Barry
On 08/07/2024 12:36, Barry Song wrote: > On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts <ryan.roberts@arm.com> wrote: >> >> The legacy PMD-sized THP counters at /proc/vmstat include >> thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which >> rather confusingly refer to shmem THP and do not include any other types >> of file pages. This is inconsistent since in most other places in the >> kernel, THP counters are explicitly separated for anon, shmem and file >> flavours. However, we are stuck with it since it constitutes a user ABI. >> >> Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for >> anonymous shmem") added equivalent mTHP stats for shmem, keeping the >> same "file_" prefix in the names. But in future, we may want to add >> extra stats to cover actual file pages, at which point, it would all >> become very confusing. >> >> So let's take the opportunity to rename these new counters "shmem_" >> before the change makes it upstream and the ABI becomes immutable. > > Personally, I think this approach is much clearer. However, I recall > we discussed this > before [1], and it seems that inconsistency is a concern? Embarrassingly, I don't recall that converstation at all :-| but at least what I said then is consistent with what I've done in this patch. I think David's conclusion from that thread was to call them FILE_, and add both shmem and pagecache counts to those counters, meaning we can keep the same name as legacy THP counters. But those legacy THP counters only count shmem, and I don't think we would get away with adding pagecache counts to those at this point? (argument: they have been around for long time and there is a risk that user space relies on them and if they were to dramatically increase due to pagecache addition now that could break things). In that case, there is still inconsistency, but its worse; the names are consistent but the semantics are inconsistent. So my vote is to change to SHMEM_ as per this patch :) > > [1] https://lore.kernel.org/linux-mm/05d0096e4ec3e572d1d52d33a31a661321ac1551.1713755580.git.baolin.wang@linux.alibaba.com/ > > >> >> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> >> --- >> >> Hi All, >> >> Applies on top of today's mm-unstable (2073cda629a4) and tested with mm >> selftests; no regressions observed. >> >> The backstory here is that I'd like to introduce some counters for regular file >> folio allocations to observe how often large folio allocation succeeds, but >> these shmem counters are named "file" which is going to make things confusing. >> So hoping to solve that before commit 66f44583f9b6 ("mm: shmem: add mTHP >> counters for anonymous shmem") goes upstream (it is currently in mm-stable). >> >> Admittedly, this change means the mTHP stat names are not the same as the legacy >> PMD-size THP names, but I think that's a smaller issue than having "file_" mTHP >> stats that only count shmem, then having to introduce "file2_" or "pgcache_" >> stats for the regular file memory, which is even more inconsistent IMHO. I guess >> the alternative is to count both shmem and file in these mTHP stats (that's how >> they were documented anyway) but I think it's better to be able to consider them >> separately like we do for all the other counters. >> >> Thanks, >> Ryan >> >> Documentation/admin-guide/mm/transhuge.rst | 12 ++++++------ >> include/linux/huge_mm.h | 6 +++--- >> mm/huge_memory.c | 12 ++++++------ >> mm/shmem.c | 8 ++++---- >> 4 files changed, 19 insertions(+), 19 deletions(-) >> >> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst >> index 747c811ee8f1..8b891689fc13 100644 >> --- a/Documentation/admin-guide/mm/transhuge.rst >> +++ b/Documentation/admin-guide/mm/transhuge.rst >> @@ -496,16 +496,16 @@ swpout_fallback >> Usually because failed to allocate some continuous swap space >> for the huge page. >> >> -file_alloc >> - is incremented every time a file huge page is successfully >> +shmem_alloc >> + is incremented every time a shmem huge page is successfully >> allocated. >> >> -file_fallback >> - is incremented if a file huge page is attempted to be allocated >> +shmem_fallback >> + is incremented if a shmem huge page is attempted to be allocated >> but fails and instead falls back to using small pages. >> >> -file_fallback_charge >> - is incremented if a file huge page cannot be charged and instead >> +shmem_fallback_charge >> + is incremented if a shmem huge page cannot be charged and instead >> falls back to using small pages even though the allocation was >> successful. >> >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> index acb6ac24a07e..cff002be83eb 100644 >> --- a/include/linux/huge_mm.h >> +++ b/include/linux/huge_mm.h >> @@ -269,9 +269,9 @@ enum mthp_stat_item { >> MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE, >> MTHP_STAT_SWPOUT, >> MTHP_STAT_SWPOUT_FALLBACK, >> - MTHP_STAT_FILE_ALLOC, >> - MTHP_STAT_FILE_FALLBACK, >> - MTHP_STAT_FILE_FALLBACK_CHARGE, >> + MTHP_STAT_SHMEM_ALLOC, >> + MTHP_STAT_SHMEM_FALLBACK, >> + MTHP_STAT_SHMEM_FALLBACK_CHARGE, >> MTHP_STAT_SPLIT, >> MTHP_STAT_SPLIT_FAILED, >> MTHP_STAT_SPLIT_DEFERRED, >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 9ec64aa2be94..f9696c94e211 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -568,9 +568,9 @@ DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK); >> DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE); >> DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT); >> DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK); >> -DEFINE_MTHP_STAT_ATTR(file_alloc, MTHP_STAT_FILE_ALLOC); >> -DEFINE_MTHP_STAT_ATTR(file_fallback, MTHP_STAT_FILE_FALLBACK); >> -DEFINE_MTHP_STAT_ATTR(file_fallback_charge, MTHP_STAT_FILE_FALLBACK_CHARGE); >> +DEFINE_MTHP_STAT_ATTR(shmem_alloc, MTHP_STAT_SHMEM_ALLOC); >> +DEFINE_MTHP_STAT_ATTR(shmem_fallback, MTHP_STAT_SHMEM_FALLBACK); >> +DEFINE_MTHP_STAT_ATTR(shmem_fallback_charge, MTHP_STAT_SHMEM_FALLBACK_CHARGE); >> DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT); >> DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED); >> DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED); >> @@ -581,9 +581,9 @@ static struct attribute *stats_attrs[] = { >> &anon_fault_fallback_charge_attr.attr, >> &swpout_attr.attr, >> &swpout_fallback_attr.attr, >> - &file_alloc_attr.attr, >> - &file_fallback_attr.attr, >> - &file_fallback_charge_attr.attr, >> + &shmem_alloc_attr.attr, >> + &shmem_fallback_attr.attr, >> + &shmem_fallback_charge_attr.attr, >> &split_attr.attr, >> &split_failed_attr.attr, >> &split_deferred_attr.attr, >> diff --git a/mm/shmem.c b/mm/shmem.c >> index 921d59c3d669..f24dfbd387ba 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -1777,7 +1777,7 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, >> if (pages == HPAGE_PMD_NR) >> count_vm_event(THP_FILE_FALLBACK); >> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >> - count_mthp_stat(order, MTHP_STAT_FILE_FALLBACK); >> + count_mthp_stat(order, MTHP_STAT_SHMEM_FALLBACK); >> #endif >> order = next_order(&suitable_orders, order); >> } >> @@ -1804,8 +1804,8 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, >> count_vm_event(THP_FILE_FALLBACK_CHARGE); >> } >> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >> - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK); >> - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK_CHARGE); >> + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK); >> + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK_CHARGE); >> #endif >> } >> goto unlock; >> @@ -2181,7 +2181,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index, >> if (folio_test_pmd_mappable(folio)) >> count_vm_event(THP_FILE_ALLOC); >> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >> - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_ALLOC); >> + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_ALLOC); >> #endif >> goto alloced; >> } >> -- >> 2.43.0 >> > > Thanks > Barry
On 08.07.24 14:29, Ryan Roberts wrote: > On 08/07/2024 12:36, Barry Song wrote: >> On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts <ryan.roberts@arm.com> wrote: >>> >>> The legacy PMD-sized THP counters at /proc/vmstat include >>> thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which >>> rather confusingly refer to shmem THP and do not include any other types >>> of file pages. This is inconsistent since in most other places in the >>> kernel, THP counters are explicitly separated for anon, shmem and file >>> flavours. However, we are stuck with it since it constitutes a user ABI. >>> >>> Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for >>> anonymous shmem") added equivalent mTHP stats for shmem, keeping the >>> same "file_" prefix in the names. But in future, we may want to add >>> extra stats to cover actual file pages, at which point, it would all >>> become very confusing. >>> >>> So let's take the opportunity to rename these new counters "shmem_" >>> before the change makes it upstream and the ABI becomes immutable. >> >> Personally, I think this approach is much clearer. However, I recall >> we discussed this >> before [1], and it seems that inconsistency is a concern? > > Embarrassingly, I don't recall that converstation at all :-| but at least what I > said then is consistent with what I've done in this patch. > > I think David's conclusion from that thread was to call them FILE_, and add both > shmem and pagecache counts to those counters, meaning we can keep the same name > as legacy THP counters. But those legacy THP counters only count shmem, and I > don't think we would get away with adding pagecache counts to those at this > point? (argument: they have been around for long time and there is a risk that > user space relies on them and if they were to dramatically increase due to > pagecache addition now that could break things). In that case, there is still > inconsistency, but its worse; the names are consistent but the semantics are > inconsistent. > > So my vote is to change to SHMEM_ as per this patch :) I also forgot most of the discussion, but these 3 legacy counters are really only (currently) incremented for shmem. I think my idea was to keep everything as FILE_ for now, maybe at some point make the pagecache also use them, and then maybe have separate FILE_ + SHMEM_. But yeah, likely it's best to only have "shmem" here for now, because who knows what we can actually change about the legacy counters. But it's always though messing with legacy stuff that is clearly suboptimal ...
On 2024/7/8 20:29, Ryan Roberts wrote: > On 08/07/2024 12:36, Barry Song wrote: >> On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts <ryan.roberts@arm.com> wrote: >>> >>> The legacy PMD-sized THP counters at /proc/vmstat include >>> thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which >>> rather confusingly refer to shmem THP and do not include any other types >>> of file pages. This is inconsistent since in most other places in the >>> kernel, THP counters are explicitly separated for anon, shmem and file >>> flavours. However, we are stuck with it since it constitutes a user ABI. >>> >>> Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for >>> anonymous shmem") added equivalent mTHP stats for shmem, keeping the >>> same "file_" prefix in the names. But in future, we may want to add >>> extra stats to cover actual file pages, at which point, it would all >>> become very confusing. >>> >>> So let's take the opportunity to rename these new counters "shmem_" >>> before the change makes it upstream and the ABI becomes immutable. >> >> Personally, I think this approach is much clearer. However, I recall >> we discussed this >> before [1], and it seems that inconsistency is a concern? > > Embarrassingly, I don't recall that converstation at all :-| but at least what I > said then is consistent with what I've done in this patch. > > I think David's conclusion from that thread was to call them FILE_, and add both > shmem and pagecache counts to those counters, meaning we can keep the same name > as legacy THP counters. But those legacy THP counters only count shmem, and I > don't think we would get away with adding pagecache counts to those at this > point? (argument: they have been around for long time and there is a risk that > user space relies on them and if they were to dramatically increase due to > pagecache addition now that could break things). In that case, there is still > inconsistency, but its worse; the names are consistent but the semantics are > inconsistent. > > So my vote is to change to SHMEM_ as per this patch :) > >> >> [1] https://lore.kernel.org/linux-mm/05d0096e4ec3e572d1d52d33a31a661321ac1551.1713755580.git.baolin.wang@linux.alibaba.com/ My original preference was also for SHMEM-specific counters :) So feel free to add: Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
On Tue, Jul 9, 2024 at 4:50 AM David Hildenbrand <david@redhat.com> wrote: > > On 08.07.24 14:29, Ryan Roberts wrote: > > On 08/07/2024 12:36, Barry Song wrote: > >> On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts <ryan.roberts@arm.com> wrote: > >>> > >>> The legacy PMD-sized THP counters at /proc/vmstat include > >>> thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which > >>> rather confusingly refer to shmem THP and do not include any other types > >>> of file pages. This is inconsistent since in most other places in the > >>> kernel, THP counters are explicitly separated for anon, shmem and file > >>> flavours. However, we are stuck with it since it constitutes a user ABI. > >>> > >>> Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for > >>> anonymous shmem") added equivalent mTHP stats for shmem, keeping the > >>> same "file_" prefix in the names. But in future, we may want to add > >>> extra stats to cover actual file pages, at which point, it would all > >>> become very confusing. > >>> > >>> So let's take the opportunity to rename these new counters "shmem_" > >>> before the change makes it upstream and the ABI becomes immutable. > >> > >> Personally, I think this approach is much clearer. However, I recall > >> we discussed this > >> before [1], and it seems that inconsistency is a concern? > > > > Embarrassingly, I don't recall that converstation at all :-| but at least what I > > said then is consistent with what I've done in this patch. > > > > I think David's conclusion from that thread was to call them FILE_, and add both > > shmem and pagecache counts to those counters, meaning we can keep the same name > > as legacy THP counters. But those legacy THP counters only count shmem, and I > > don't think we would get away with adding pagecache counts to those at this > > point? (argument: they have been around for long time and there is a risk that > > user space relies on them and if they were to dramatically increase due to > > pagecache addition now that could break things). In that case, there is still > > inconsistency, but its worse; the names are consistent but the semantics are > > inconsistent. > > > > So my vote is to change to SHMEM_ as per this patch :) > > I also forgot most of the discussion, but these 3 legacy counters are > really only (currently) incremented for shmem. I think my idea was to > keep everything as FILE_ for now, maybe at some point make the pagecache > also use them, and then maybe have separate FILE_ + SHMEM_. > > But yeah, likely it's best to only have "shmem" here for now, because > who knows what we can actually change about the legacy counters. But > it's always though messing with legacy stuff that is clearly suboptimal ... Couldn't agree more! It's never an easy task to handle such matters :) Perhaps, the time has come for us to separate FILE_ and SHMEM_. Thanks, Lance > > -- > Cheers, > > David / dhildenb >
On Mon, Jul 8, 2024 at 7:24 PM Ryan Roberts <ryan.roberts@arm.com> wrote: > > The legacy PMD-sized THP counters at /proc/vmstat include > thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which > rather confusingly refer to shmem THP and do not include any other types > of file pages. This is inconsistent since in most other places in the > kernel, THP counters are explicitly separated for anon, shmem and file > flavours. However, we are stuck with it since it constitutes a user ABI. > > Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for > anonymous shmem") added equivalent mTHP stats for shmem, keeping the > same "file_" prefix in the names. But in future, we may want to add > extra stats to cover actual file pages, at which point, it would all > become very confusing. > > So let's take the opportunity to rename these new counters "shmem_" > before the change makes it upstream and the ABI becomes immutable. > > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> LGTM. Feel free to add: Reviewed-by: Lance Yang <ioworker0@gmail.com> Thanks, Lance > --- > > Hi All, > > Applies on top of today's mm-unstable (2073cda629a4) and tested with mm > selftests; no regressions observed. > > The backstory here is that I'd like to introduce some counters for regular file > folio allocations to observe how often large folio allocation succeeds, but > these shmem counters are named "file" which is going to make things confusing. > So hoping to solve that before commit 66f44583f9b6 ("mm: shmem: add mTHP > counters for anonymous shmem") goes upstream (it is currently in mm-stable). > > Admittedly, this change means the mTHP stat names are not the same as the legacy > PMD-size THP names, but I think that's a smaller issue than having "file_" mTHP > stats that only count shmem, then having to introduce "file2_" or "pgcache_" > stats for the regular file memory, which is even more inconsistent IMHO. I guess > the alternative is to count both shmem and file in these mTHP stats (that's how > they were documented anyway) but I think it's better to be able to consider them > separately like we do for all the other counters. > > Thanks, > Ryan > > Documentation/admin-guide/mm/transhuge.rst | 12 ++++++------ > include/linux/huge_mm.h | 6 +++--- > mm/huge_memory.c | 12 ++++++------ > mm/shmem.c | 8 ++++---- > 4 files changed, 19 insertions(+), 19 deletions(-) > > diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst > index 747c811ee8f1..8b891689fc13 100644 > --- a/Documentation/admin-guide/mm/transhuge.rst > +++ b/Documentation/admin-guide/mm/transhuge.rst > @@ -496,16 +496,16 @@ swpout_fallback > Usually because failed to allocate some continuous swap space > for the huge page. > > -file_alloc > - is incremented every time a file huge page is successfully > +shmem_alloc > + is incremented every time a shmem huge page is successfully > allocated. > > -file_fallback > - is incremented if a file huge page is attempted to be allocated > +shmem_fallback > + is incremented if a shmem huge page is attempted to be allocated > but fails and instead falls back to using small pages. > > -file_fallback_charge > - is incremented if a file huge page cannot be charged and instead > +shmem_fallback_charge > + is incremented if a shmem huge page cannot be charged and instead > falls back to using small pages even though the allocation was > successful. > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index acb6ac24a07e..cff002be83eb 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -269,9 +269,9 @@ enum mthp_stat_item { > MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE, > MTHP_STAT_SWPOUT, > MTHP_STAT_SWPOUT_FALLBACK, > - MTHP_STAT_FILE_ALLOC, > - MTHP_STAT_FILE_FALLBACK, > - MTHP_STAT_FILE_FALLBACK_CHARGE, > + MTHP_STAT_SHMEM_ALLOC, > + MTHP_STAT_SHMEM_FALLBACK, > + MTHP_STAT_SHMEM_FALLBACK_CHARGE, > MTHP_STAT_SPLIT, > MTHP_STAT_SPLIT_FAILED, > MTHP_STAT_SPLIT_DEFERRED, > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 9ec64aa2be94..f9696c94e211 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -568,9 +568,9 @@ DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK); > DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE); > DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT); > DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK); > -DEFINE_MTHP_STAT_ATTR(file_alloc, MTHP_STAT_FILE_ALLOC); > -DEFINE_MTHP_STAT_ATTR(file_fallback, MTHP_STAT_FILE_FALLBACK); > -DEFINE_MTHP_STAT_ATTR(file_fallback_charge, MTHP_STAT_FILE_FALLBACK_CHARGE); > +DEFINE_MTHP_STAT_ATTR(shmem_alloc, MTHP_STAT_SHMEM_ALLOC); > +DEFINE_MTHP_STAT_ATTR(shmem_fallback, MTHP_STAT_SHMEM_FALLBACK); > +DEFINE_MTHP_STAT_ATTR(shmem_fallback_charge, MTHP_STAT_SHMEM_FALLBACK_CHARGE); > DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT); > DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED); > DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED); > @@ -581,9 +581,9 @@ static struct attribute *stats_attrs[] = { > &anon_fault_fallback_charge_attr.attr, > &swpout_attr.attr, > &swpout_fallback_attr.attr, > - &file_alloc_attr.attr, > - &file_fallback_attr.attr, > - &file_fallback_charge_attr.attr, > + &shmem_alloc_attr.attr, > + &shmem_fallback_attr.attr, > + &shmem_fallback_charge_attr.attr, > &split_attr.attr, > &split_failed_attr.attr, > &split_deferred_attr.attr, > diff --git a/mm/shmem.c b/mm/shmem.c > index 921d59c3d669..f24dfbd387ba 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1777,7 +1777,7 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, > if (pages == HPAGE_PMD_NR) > count_vm_event(THP_FILE_FALLBACK); > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > - count_mthp_stat(order, MTHP_STAT_FILE_FALLBACK); > + count_mthp_stat(order, MTHP_STAT_SHMEM_FALLBACK); > #endif > order = next_order(&suitable_orders, order); > } > @@ -1804,8 +1804,8 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, > count_vm_event(THP_FILE_FALLBACK_CHARGE); > } > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK); > - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK_CHARGE); > + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK); > + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK_CHARGE); > #endif > } > goto unlock; > @@ -2181,7 +2181,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index, > if (folio_test_pmd_mappable(folio)) > count_vm_event(THP_FILE_ALLOC); > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_ALLOC); > + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_ALLOC); > #endif > goto alloced; > } > -- > 2.43.0 >
On 08/07/2024 21:50, David Hildenbrand wrote: > On 08.07.24 14:29, Ryan Roberts wrote: >> On 08/07/2024 12:36, Barry Song wrote: >>> On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts <ryan.roberts@arm.com> wrote: >>>> >>>> The legacy PMD-sized THP counters at /proc/vmstat include >>>> thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which >>>> rather confusingly refer to shmem THP and do not include any other types >>>> of file pages. This is inconsistent since in most other places in the >>>> kernel, THP counters are explicitly separated for anon, shmem and file >>>> flavours. However, we are stuck with it since it constitutes a user ABI. >>>> >>>> Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for >>>> anonymous shmem") added equivalent mTHP stats for shmem, keeping the >>>> same "file_" prefix in the names. But in future, we may want to add >>>> extra stats to cover actual file pages, at which point, it would all >>>> become very confusing. >>>> >>>> So let's take the opportunity to rename these new counters "shmem_" >>>> before the change makes it upstream and the ABI becomes immutable. >>> >>> Personally, I think this approach is much clearer. However, I recall >>> we discussed this >>> before [1], and it seems that inconsistency is a concern? >> >> Embarrassingly, I don't recall that converstation at all :-| but at least what I >> said then is consistent with what I've done in this patch. >> >> I think David's conclusion from that thread was to call them FILE_, and add both >> shmem and pagecache counts to those counters, meaning we can keep the same name >> as legacy THP counters. But those legacy THP counters only count shmem, and I >> don't think we would get away with adding pagecache counts to those at this >> point? (argument: they have been around for long time and there is a risk that >> user space relies on them and if they were to dramatically increase due to >> pagecache addition now that could break things). In that case, there is still >> inconsistency, but its worse; the names are consistent but the semantics are >> inconsistent. >> >> So my vote is to change to SHMEM_ as per this patch :) > > I also forgot most of the discussion, but these 3 legacy counters are really > only (currently) incremented for shmem. I think my idea was to keep everything > as FILE_ for now, maybe at some point make the pagecache also use them, and then > maybe have separate FILE_ + SHMEM_. > > But yeah, likely it's best to only have "shmem" here for now, because who knows > what we can actually change about the legacy counters. But it's always though > messing with legacy stuff that is clearly suboptimal ... Sorry David, I've read your response a bunch of times and am still not completely sure what you are advocating for. To make my proposal crystal clear, I think we should leave the legacy counters alone - neither change their name nor what they count (which is _only_ shmem). I think we should rename the new mTHP counters to "shmem" and have them continue to only count shmem. Then additionally, I think we should introduce new "file" mTHP counters that count the page cache allocations (that's a future set of patches, which I'm working on together with user controls to determine which mTHP sizes can be used by page cache). As suggested by Barry, I propose to also improve the documentation for the legacy counters to make it clear that dispite their name being "file" they are actually counting "shmem". I'll do this for v2. David, would you support this approach? If so, I'd like to push this forwards asap so that it gets into v6.11 to avoid ever exposing the mthp counters with the "file" name. Thanks, Ryan
On 09.07.24 09:47, Ryan Roberts wrote: > On 08/07/2024 21:50, David Hildenbrand wrote: >> On 08.07.24 14:29, Ryan Roberts wrote: >>> On 08/07/2024 12:36, Barry Song wrote: >>>> On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts <ryan.roberts@arm.com> wrote: >>>>> >>>>> The legacy PMD-sized THP counters at /proc/vmstat include >>>>> thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which >>>>> rather confusingly refer to shmem THP and do not include any other types >>>>> of file pages. This is inconsistent since in most other places in the >>>>> kernel, THP counters are explicitly separated for anon, shmem and file >>>>> flavours. However, we are stuck with it since it constitutes a user ABI. >>>>> >>>>> Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for >>>>> anonymous shmem") added equivalent mTHP stats for shmem, keeping the >>>>> same "file_" prefix in the names. But in future, we may want to add >>>>> extra stats to cover actual file pages, at which point, it would all >>>>> become very confusing. >>>>> >>>>> So let's take the opportunity to rename these new counters "shmem_" >>>>> before the change makes it upstream and the ABI becomes immutable. >>>> >>>> Personally, I think this approach is much clearer. However, I recall >>>> we discussed this >>>> before [1], and it seems that inconsistency is a concern? >>> >>> Embarrassingly, I don't recall that converstation at all :-| but at least what I >>> said then is consistent with what I've done in this patch. >>> >>> I think David's conclusion from that thread was to call them FILE_, and add both >>> shmem and pagecache counts to those counters, meaning we can keep the same name >>> as legacy THP counters. But those legacy THP counters only count shmem, and I >>> don't think we would get away with adding pagecache counts to those at this >>> point? (argument: they have been around for long time and there is a risk that >>> user space relies on them and if they were to dramatically increase due to >>> pagecache addition now that could break things). In that case, there is still >>> inconsistency, but its worse; the names are consistent but the semantics are >>> inconsistent. >>> >>> So my vote is to change to SHMEM_ as per this patch :) >> >> I also forgot most of the discussion, but these 3 legacy counters are really >> only (currently) incremented for shmem. I think my idea was to keep everything >> as FILE_ for now, maybe at some point make the pagecache also use them, and then >> maybe have separate FILE_ + SHMEM_. >> >> But yeah, likely it's best to only have "shmem" here for now, because who knows >> what we can actually change about the legacy counters. But it's always though >> messing with legacy stuff that is clearly suboptimal ... > > Sorry David, I've read your response a bunch of times and am still not > completely sure what you are advocating for. > > To make my proposal crystal clear, I think we should leave the legacy counters > alone - neither change their name nor what they count (which is _only_ shmem). I > think we should rename the new mTHP counters to "shmem" and have them continue > to only count shmem. Then additionally, I think we should introduce new "file" > mTHP counters that count the page cache allocations (that's a future set of > patches, which I'm working on together with user controls to determine which > mTHP sizes can be used by page cache). > > As suggested by Barry, I propose to also improve the documentation for the > legacy counters to make it clear that dispite their name being "file" they are > actually counting "shmem". I'll do this for v2. Yes, and please. Likely we should document for the legacy ones (if not already done) that they only track PMD-sized THPs. > > David, would you support this approach? If so, I'd like to push this forwards > asap so that it gets into v6.11 to avoid ever exposing the mthp counters with > the "file" name. Yes, sorry for not being clear.
On 09/07/2024 08:54, David Hildenbrand wrote: > On 09.07.24 09:47, Ryan Roberts wrote: >> On 08/07/2024 21:50, David Hildenbrand wrote: >>> On 08.07.24 14:29, Ryan Roberts wrote: >>>> On 08/07/2024 12:36, Barry Song wrote: >>>>> On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts <ryan.roberts@arm.com> wrote: >>>>>> >>>>>> The legacy PMD-sized THP counters at /proc/vmstat include >>>>>> thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which >>>>>> rather confusingly refer to shmem THP and do not include any other types >>>>>> of file pages. This is inconsistent since in most other places in the >>>>>> kernel, THP counters are explicitly separated for anon, shmem and file >>>>>> flavours. However, we are stuck with it since it constitutes a user ABI. >>>>>> >>>>>> Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for >>>>>> anonymous shmem") added equivalent mTHP stats for shmem, keeping the >>>>>> same "file_" prefix in the names. But in future, we may want to add >>>>>> extra stats to cover actual file pages, at which point, it would all >>>>>> become very confusing. >>>>>> >>>>>> So let's take the opportunity to rename these new counters "shmem_" >>>>>> before the change makes it upstream and the ABI becomes immutable. >>>>> >>>>> Personally, I think this approach is much clearer. However, I recall >>>>> we discussed this >>>>> before [1], and it seems that inconsistency is a concern? >>>> >>>> Embarrassingly, I don't recall that converstation at all :-| but at least >>>> what I >>>> said then is consistent with what I've done in this patch. >>>> >>>> I think David's conclusion from that thread was to call them FILE_, and add >>>> both >>>> shmem and pagecache counts to those counters, meaning we can keep the same name >>>> as legacy THP counters. But those legacy THP counters only count shmem, and I >>>> don't think we would get away with adding pagecache counts to those at this >>>> point? (argument: they have been around for long time and there is a risk that >>>> user space relies on them and if they were to dramatically increase due to >>>> pagecache addition now that could break things). In that case, there is still >>>> inconsistency, but its worse; the names are consistent but the semantics are >>>> inconsistent. >>>> >>>> So my vote is to change to SHMEM_ as per this patch :) >>> >>> I also forgot most of the discussion, but these 3 legacy counters are really >>> only (currently) incremented for shmem. I think my idea was to keep everything >>> as FILE_ for now, maybe at some point make the pagecache also use them, and then >>> maybe have separate FILE_ + SHMEM_. >>> >>> But yeah, likely it's best to only have "shmem" here for now, because who knows >>> what we can actually change about the legacy counters. But it's always though >>> messing with legacy stuff that is clearly suboptimal ... >> >> Sorry David, I've read your response a bunch of times and am still not >> completely sure what you are advocating for. >> >> To make my proposal crystal clear, I think we should leave the legacy counters >> alone - neither change their name nor what they count (which is _only_ shmem). I >> think we should rename the new mTHP counters to "shmem" and have them continue >> to only count shmem. Then additionally, I think we should introduce new "file" >> mTHP counters that count the page cache allocations (that's a future set of >> patches, which I'm working on together with user controls to determine which >> mTHP sizes can be used by page cache). >> >> As suggested by Barry, I propose to also improve the documentation for the >> legacy counters to make it clear that dispite their name being "file" they are >> actually counting "shmem". I'll do this for v2. > > Yes, and please. Likely we should document for the legacy ones (if not already > done) that they only track PMD-sized THPs. The PMD-ness is already documented for the legacy counters IIRC, but I'll double check. > >> >> David, would you support this approach? If so, I'd like to push this forwards >> asap so that it gets into v6.11 to avoid ever exposing the mthp counters with >> the "file" name. > > Yes, sorry for not being clear. No worries, it sounds like at least Lance understood exectly what you were saying, so likely I'm just being obtuse. Anyway, I'll respin with the docs improvements and get v2 out shortly. Thanks, Ryan
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index 747c811ee8f1..8b891689fc13 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -496,16 +496,16 @@ swpout_fallback Usually because failed to allocate some continuous swap space for the huge page. -file_alloc - is incremented every time a file huge page is successfully +shmem_alloc + is incremented every time a shmem huge page is successfully allocated. -file_fallback - is incremented if a file huge page is attempted to be allocated +shmem_fallback + is incremented if a shmem huge page is attempted to be allocated but fails and instead falls back to using small pages. -file_fallback_charge - is incremented if a file huge page cannot be charged and instead +shmem_fallback_charge + is incremented if a shmem huge page cannot be charged and instead falls back to using small pages even though the allocation was successful. diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index acb6ac24a07e..cff002be83eb 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -269,9 +269,9 @@ enum mthp_stat_item { MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE, MTHP_STAT_SWPOUT, MTHP_STAT_SWPOUT_FALLBACK, - MTHP_STAT_FILE_ALLOC, - MTHP_STAT_FILE_FALLBACK, - MTHP_STAT_FILE_FALLBACK_CHARGE, + MTHP_STAT_SHMEM_ALLOC, + MTHP_STAT_SHMEM_FALLBACK, + MTHP_STAT_SHMEM_FALLBACK_CHARGE, MTHP_STAT_SPLIT, MTHP_STAT_SPLIT_FAILED, MTHP_STAT_SPLIT_DEFERRED, diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 9ec64aa2be94..f9696c94e211 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -568,9 +568,9 @@ DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK); DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE); DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT); DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK); -DEFINE_MTHP_STAT_ATTR(file_alloc, MTHP_STAT_FILE_ALLOC); -DEFINE_MTHP_STAT_ATTR(file_fallback, MTHP_STAT_FILE_FALLBACK); -DEFINE_MTHP_STAT_ATTR(file_fallback_charge, MTHP_STAT_FILE_FALLBACK_CHARGE); +DEFINE_MTHP_STAT_ATTR(shmem_alloc, MTHP_STAT_SHMEM_ALLOC); +DEFINE_MTHP_STAT_ATTR(shmem_fallback, MTHP_STAT_SHMEM_FALLBACK); +DEFINE_MTHP_STAT_ATTR(shmem_fallback_charge, MTHP_STAT_SHMEM_FALLBACK_CHARGE); DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT); DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED); DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED); @@ -581,9 +581,9 @@ static struct attribute *stats_attrs[] = { &anon_fault_fallback_charge_attr.attr, &swpout_attr.attr, &swpout_fallback_attr.attr, - &file_alloc_attr.attr, - &file_fallback_attr.attr, - &file_fallback_charge_attr.attr, + &shmem_alloc_attr.attr, + &shmem_fallback_attr.attr, + &shmem_fallback_charge_attr.attr, &split_attr.attr, &split_failed_attr.attr, &split_deferred_attr.attr, diff --git a/mm/shmem.c b/mm/shmem.c index 921d59c3d669..f24dfbd387ba 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1777,7 +1777,7 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, if (pages == HPAGE_PMD_NR) count_vm_event(THP_FILE_FALLBACK); #ifdef CONFIG_TRANSPARENT_HUGEPAGE - count_mthp_stat(order, MTHP_STAT_FILE_FALLBACK); + count_mthp_stat(order, MTHP_STAT_SHMEM_FALLBACK); #endif order = next_order(&suitable_orders, order); } @@ -1804,8 +1804,8 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf, count_vm_event(THP_FILE_FALLBACK_CHARGE); } #ifdef CONFIG_TRANSPARENT_HUGEPAGE - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK); - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK_CHARGE); + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK); + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK_CHARGE); #endif } goto unlock; @@ -2181,7 +2181,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index, if (folio_test_pmd_mappable(folio)) count_vm_event(THP_FILE_ALLOC); #ifdef CONFIG_TRANSPARENT_HUGEPAGE - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_ALLOC); + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_ALLOC); #endif goto alloced; }
The legacy PMD-sized THP counters at /proc/vmstat include thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which rather confusingly refer to shmem THP and do not include any other types of file pages. This is inconsistent since in most other places in the kernel, THP counters are explicitly separated for anon, shmem and file flavours. However, we are stuck with it since it constitutes a user ABI. Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for anonymous shmem") added equivalent mTHP stats for shmem, keeping the same "file_" prefix in the names. But in future, we may want to add extra stats to cover actual file pages, at which point, it would all become very confusing. So let's take the opportunity to rename these new counters "shmem_" before the change makes it upstream and the ABI becomes immutable. Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> --- Hi All, Applies on top of today's mm-unstable (2073cda629a4) and tested with mm selftests; no regressions observed. The backstory here is that I'd like to introduce some counters for regular file folio allocations to observe how often large folio allocation succeeds, but these shmem counters are named "file" which is going to make things confusing. So hoping to solve that before commit 66f44583f9b6 ("mm: shmem: add mTHP counters for anonymous shmem") goes upstream (it is currently in mm-stable). Admittedly, this change means the mTHP stat names are not the same as the legacy PMD-size THP names, but I think that's a smaller issue than having "file_" mTHP stats that only count shmem, then having to introduce "file2_" or "pgcache_" stats for the regular file memory, which is even more inconsistent IMHO. I guess the alternative is to count both shmem and file in these mTHP stats (that's how they were documented anyway) but I think it's better to be able to consider them separately like we do for all the other counters. Thanks, Ryan Documentation/admin-guide/mm/transhuge.rst | 12 ++++++------ include/linux/huge_mm.h | 6 +++--- mm/huge_memory.c | 12 ++++++------ mm/shmem.c | 8 ++++---- 4 files changed, 19 insertions(+), 19 deletions(-) -- 2.43.0