| Message ID | 1634278529-16983-1-git-send-email-huangzhaoyang@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: skip current when memcg reclaim | expand |
On Fri, 15 Oct 2021 14:15:29 +0800 Huangzhaoyang <huangzhaoyang@gmail.com> wrote: > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > Sibling thread of the same process could refault the reclaimed pages > in the same time, which would be typical in None global reclaim and > introduce thrashing. "None" -> "node", I assume? > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) > sc->memcg_low_skipped = 1; > continue; > } > + /* > + * Don't bother current when its memcg is below low > + */ The comment explains what the code is doing, but the code itself already does this. Please can we have a comment that explains *why* the code is doing this? > + if (get_mem_cgroup_from_mm(current->mm) == memcg) > + continue; > memcg_memory_event(memcg, MEMCG_LOW); > }
On Sat, Oct 16, 2021 at 4:00 AM Andrew Morton <akpm@linux-foundation.org> wrote: > > On Fri, 15 Oct 2021 14:15:29 +0800 Huangzhaoyang <huangzhaoyang@gmail.com> wrote: > > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > > Sibling thread of the same process could refault the reclaimed pages > > in the same time, which would be typical in None global reclaim and > > introduce thrashing. > > "None" -> "node", I assume? > > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) > > sc->memcg_low_skipped = 1; > > continue; > > } > > + /* > > + * Don't bother current when its memcg is below low > > + */ > > The comment explains what the code is doing, but the code itself > already does this. Please can we have a comment that explains *why* > the code is doing this? We find that the patch help direct reclaiming bail out early and eliminate page thrashing for some scenarios(etc APP start on android). The case could be worse if each APP possess a unique memcg(pages on current's lru are reclaimed more than global reclaim) > > > > + if (get_mem_cgroup_from_mm(current->mm) == memcg) > > + continue; > > memcg_memory_event(memcg, MEMCG_LOW); > > } >
On Sat, 16 Oct 2021 10:28:54 +0800 Zhaoyang Huang <huangzhaoyang@gmail.com> wrote: > On Sat, Oct 16, 2021 at 4:00 AM Andrew Morton <akpm@linux-foundation.org> wrote: > > > > On Fri, 15 Oct 2021 14:15:29 +0800 Huangzhaoyang <huangzhaoyang@gmail.com> wrote: > > > > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > > > > Sibling thread of the same process could refault the reclaimed pages > > > in the same time, which would be typical in None global reclaim and > > > introduce thrashing. > > > > "None" -> "node", I assume? > > > > > --- a/mm/vmscan.c > > > +++ b/mm/vmscan.c > > > @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) > > > sc->memcg_low_skipped = 1; > > > continue; > > > } > > > + /* > > > + * Don't bother current when its memcg is below low > > > + */ > > > > The comment explains what the code is doing, but the code itself > > already does this. Please can we have a comment that explains *why* > > the code is doing this? > We find that the patch help direct reclaiming bail out early and > eliminate page thrashing for some scenarios(etc APP start on android). > The case could be worse if each APP possess a unique memcg(pages on > current's lru are reclaimed more than global reclaim) What I meant was: please redo the patch with a comment which explains "why the code does this", rather than "what the code does". Also, as this is a performance enhancement, it is preferred to have some performance testing results in the changelog.
On Fri, Oct 15, 2021 at 01:00:35PM -0700, Andrew Morton wrote: > On Fri, 15 Oct 2021 14:15:29 +0800 Huangzhaoyang <huangzhaoyang@gmail.com> wrote: > > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > > Sibling thread of the same process could refault the reclaimed pages > > in the same time, which would be typical in None global reclaim and > > introduce thrashing. > > "None" -> "node", I assume? I think that's "non-global", ie memcg based.
On Sat, Oct 16, 2021 at 11:06 AM Matthew Wilcox <willy@infradead.org> wrote: > > On Fri, Oct 15, 2021 at 01:00:35PM -0700, Andrew Morton wrote: > > On Fri, 15 Oct 2021 14:15:29 +0800 Huangzhaoyang <huangzhaoyang@gmail.com> wrote: > > > > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > > > > Sibling thread of the same process could refault the reclaimed pages > > > in the same time, which would be typical in None global reclaim and > > > introduce thrashing. > > > > "None" -> "node", I assume? > > I think that's "non-global", ie memcg based. It is exactly what I mean. memcg based reclaim could be worse for page thrashing.
On Fri 15-10-21 14:15:29, Huangzhaoyang wrote: > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > Sibling thread of the same process could refault the reclaimed pages > in the same time, which would be typical in None global reclaim and > introduce thrashing. It is hard to understand what kind of problem you see (ideally along with some numbers) and how the proposed patch addresses that problem Also you are missing Signed-off-by tag (please have a look at Documentation/process/submitting-patches.rst which is much more comprehensive about the process). > --- > mm/vmscan.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 5199b96..ebbdc37 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) > sc->memcg_low_skipped = 1; > continue; > } > + /* > + * Don't bother current when its memcg is below low > + */ > + if (get_mem_cgroup_from_mm(current->mm) == memcg) > + continue; This code is executed when none of memcg in the reclaimed hierarchy could be reclaimed. Low limit is then ignored and this change is tweaking that behavior without any description of the effect. A very vague note about trashing would indicate that you have something like the following A (hiting hard limit) / \ B C Both B and C low limit protected and current task associated with B. As none of the two could be reclaimed due to soft protection yuu prefer to reclaim from C as you do not want to reclaim from the current process as that could reclaim current's working set. Correct? I would be really curious about more specifics of the used hierarchy. Thanks! > memcg_memory_event(memcg, MEMCG_LOW); > } > > -- > 1.9.1
On Mon, Oct 18, 2021 at 4:23 PM Michal Hocko <mhocko@suse.com> wrote: > > On Fri 15-10-21 14:15:29, Huangzhaoyang wrote: > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > > Sibling thread of the same process could refault the reclaimed pages > > in the same time, which would be typical in None global reclaim and > > introduce thrashing. > > It is hard to understand what kind of problem you see (ideally along > with some numbers) and how the proposed patch addresses that problem > > Also you are missing Signed-off-by tag (please have a look at > Documentation/process/submitting-patches.rst which is much more > comprehensive about the process). sorry for that, I will fix it. > > > --- > > mm/vmscan.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 5199b96..ebbdc37 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) > > sc->memcg_low_skipped = 1; > > continue; > > } > > + /* > > + * Don't bother current when its memcg is below low > > + */ > > + if (get_mem_cgroup_from_mm(current->mm) == memcg) > > + continue; > > This code is executed when none of memcg in the reclaimed hierarchy > could be reclaimed. Low limit is then ignored and this change is > tweaking that behavior without any description of the effect. A very > vague note about trashing would indicate that you have something like > the following > > A (hiting hard limit) > / \ > B C > > Both B and C low limit protected and current task associated with B. As > none of the two could be reclaimed due to soft protection yuu prefer to > reclaim from C as you do not want to reclaim from the current process as > that could reclaim current's working set. Correct? > > I would be really curious about more specifics of the used hierarchy. What I am facing is a typical scenario on Android, that is a big memory consuming APP(camera etc) launched while background filled by other processes. The hierarchy is like what you describe above where B represents the APP and memory.low is set to help warm restart. Both of kswapd and direct reclaim work together to reclaim pages under this scenario, which can cause 20MB file page delete from LRU in several second. This change could help to have current process's page escape from being reclaimed and cause page thrashing. We observed the result via systrace which shows that the Uninterruptible sleep(block on page bit) and iowait get smaller than usual. > > Thanks! > > > memcg_memory_event(memcg, MEMCG_LOW); > > } > > > > -- > > 1.9.1 > > -- > Michal Hocko > SUSE Labs
On Mon 18-10-21 17:25:23, Zhaoyang Huang wrote: > On Mon, Oct 18, 2021 at 4:23 PM Michal Hocko <mhocko@suse.com> wrote: > > > > On Fri 15-10-21 14:15:29, Huangzhaoyang wrote: > > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > > > > Sibling thread of the same process could refault the reclaimed pages > > > in the same time, which would be typical in None global reclaim and > > > introduce thrashing. > > > > It is hard to understand what kind of problem you see (ideally along > > with some numbers) and how the proposed patch addresses that problem > > > > Also you are missing Signed-off-by tag (please have a look at > > Documentation/process/submitting-patches.rst which is much more > > comprehensive about the process). > sorry for that, I will fix it. > > > > > --- > > > mm/vmscan.c | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > > index 5199b96..ebbdc37 100644 > > > --- a/mm/vmscan.c > > > +++ b/mm/vmscan.c > > > @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) > > > sc->memcg_low_skipped = 1; > > > continue; > > > } > > > + /* > > > + * Don't bother current when its memcg is below low > > > + */ > > > + if (get_mem_cgroup_from_mm(current->mm) == memcg) > > > + continue; > > > > This code is executed when none of memcg in the reclaimed hierarchy > > could be reclaimed. Low limit is then ignored and this change is > > tweaking that behavior without any description of the effect. A very > > vague note about trashing would indicate that you have something like > > the following > > > > A (hiting hard limit) > > / \ > > B C > > > > Both B and C low limit protected and current task associated with B. As > > none of the two could be reclaimed due to soft protection yuu prefer to > > reclaim from C as you do not want to reclaim from the current process as > > that could reclaim current's working set. Correct? > > > > I would be really curious about more specifics of the used hierarchy. > What I am facing is a typical scenario on Android, that is a big > memory consuming APP(camera etc) launched while background filled by > other processes. The hierarchy is like what you describe above where B > represents the APP and memory.low is set to help warm restart. Both of > kswapd and direct reclaim work together to reclaim pages under this > scenario, which can cause 20MB file page delete from LRU in several > second. This change could help to have current process's page escape > from being reclaimed and cause page thrashing. We observed the result > via systrace which shows that the Uninterruptible sleep(block on page > bit) and iowait get smaller than usual. I still have hard time to understand the exact setup and why the patch helps you. If you want to protect B more than the low limit would allow for by stealiong from C then the same thing can happen from anybody reclaiming from C so in the end there is no protection. The same would apply for any global direct memory reclaim done by a 3rd party. So I suspect that your patch just happens to work by a luck. Why both B and C have low limit setup and they both cannot be reclaimed? Isn't that a weird setup where A hard limit is too close to sum of low limits of B and C? In other words could you share a more detailed configuration you are using and some more details why both B and C have been skipped during the first pass of the reclaim?
On Mon, Oct 18, 2021 at 8:41 PM Michal Hocko <mhocko@suse.com> wrote: > > On Mon 18-10-21 17:25:23, Zhaoyang Huang wrote: > > On Mon, Oct 18, 2021 at 4:23 PM Michal Hocko <mhocko@suse.com> wrote: > > > > > > On Fri 15-10-21 14:15:29, Huangzhaoyang wrote: > > > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > > > > > > > Sibling thread of the same process could refault the reclaimed pages > > > > in the same time, which would be typical in None global reclaim and > > > > introduce thrashing. > > > > > > It is hard to understand what kind of problem you see (ideally along > > > with some numbers) and how the proposed patch addresses that problem > > > > > > Also you are missing Signed-off-by tag (please have a look at > > > Documentation/process/submitting-patches.rst which is much more > > > comprehensive about the process). > > sorry for that, I will fix it. > > > > > > > --- > > > > mm/vmscan.c | 5 +++++ > > > > 1 file changed, 5 insertions(+) > > > > > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > > > index 5199b96..ebbdc37 100644 > > > > --- a/mm/vmscan.c > > > > +++ b/mm/vmscan.c > > > > @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) > > > > sc->memcg_low_skipped = 1; > > > > continue; > > > > } > > > > + /* > > > > + * Don't bother current when its memcg is below low > > > > + */ > > > > + if (get_mem_cgroup_from_mm(current->mm) == memcg) > > > > + continue; > > > > > > This code is executed when none of memcg in the reclaimed hierarchy > > > could be reclaimed. Low limit is then ignored and this change is > > > tweaking that behavior without any description of the effect. A very > > > vague note about trashing would indicate that you have something like > > > the following > > > > > > A (hiting hard limit) > > > / \ > > > B C > > > > > > Both B and C low limit protected and current task associated with B. As > > > none of the two could be reclaimed due to soft protection yuu prefer to > > > reclaim from C as you do not want to reclaim from the current process as > > > that could reclaim current's working set. Correct? > > > > > > I would be really curious about more specifics of the used hierarchy. > > What I am facing is a typical scenario on Android, that is a big > > memory consuming APP(camera etc) launched while background filled by > > other processes. The hierarchy is like what you describe above where B > > represents the APP and memory.low is set to help warm restart. Both of > > kswapd and direct reclaim work together to reclaim pages under this > > scenario, which can cause 20MB file page delete from LRU in several > > second. This change could help to have current process's page escape > > from being reclaimed and cause page thrashing. We observed the result > > via systrace which shows that the Uninterruptible sleep(block on page > > bit) and iowait get smaller than usual. > > I still have hard time to understand the exact setup and why the patch > helps you. If you want to protect B more than the low limit would allow > for by stealiong from C then the same thing can happen from anybody > reclaiming from C so in the end there is no protection. The same would > apply for any global direct memory reclaim done by a 3rd party. So I > suspect that your patch just happens to work by a luck. B and C compete fairly and superior than others. The idea based on assuming NOT all groups will trap into direct reclaim concurrently, so we want to have the groups steal pages from the processes under root(Non-memory sensitive) or other groups with lower thresholds(high memory tolerance) or the one totally sleeping(not busy for the time being, borrow some pages). > > Why both B and C have low limit setup and they both cannot be reclaimed? > Isn't that a weird setup where A hard limit is too close to sum of low > limits of B and C? > > In other words could you share a more detailed configuration you are > using and some more details why both B and C have been skipped during > the first pass of the reclaim? My practical scenario is that important processes(vip APP etc) are placed into protected memcg and keep other processes just under root. Current introduces direct reclaim because of alloc_pages(DMA_ALLOC etc), in which the number of allocation would be much larger than low but would NOT be charged to LRU. Whereas, current also wants to keep the pages(.so files to exec) on LRU. > > -- > Michal Hocko > SUSE Labs
On Tue 19-10-21 15:11:30, Zhaoyang Huang wrote: > On Mon, Oct 18, 2021 at 8:41 PM Michal Hocko <mhocko@suse.com> wrote: > > > > On Mon 18-10-21 17:25:23, Zhaoyang Huang wrote: > > > On Mon, Oct 18, 2021 at 4:23 PM Michal Hocko <mhocko@suse.com> wrote: [...] > > > > I would be really curious about more specifics of the used hierarchy. > > > What I am facing is a typical scenario on Android, that is a big > > > memory consuming APP(camera etc) launched while background filled by > > > other processes. The hierarchy is like what you describe above where B > > > represents the APP and memory.low is set to help warm restart. Both of > > > kswapd and direct reclaim work together to reclaim pages under this > > > scenario, which can cause 20MB file page delete from LRU in several > > > second. This change could help to have current process's page escape > > > from being reclaimed and cause page thrashing. We observed the result > > > via systrace which shows that the Uninterruptible sleep(block on page > > > bit) and iowait get smaller than usual. > > > > I still have hard time to understand the exact setup and why the patch > > helps you. If you want to protect B more than the low limit would allow > > for by stealiong from C then the same thing can happen from anybody > > reclaiming from C so in the end there is no protection. The same would > > apply for any global direct memory reclaim done by a 3rd party. So I > > suspect that your patch just happens to work by a luck. > B and C compete fairly and superior than others. The idea based on > assuming NOT all groups will trap into direct reclaim concurrently, so > we want to have the groups steal pages from the processes under > root(Non-memory sensitive) or other groups with lower thresholds(high > memory tolerance) or the one totally sleeping(not busy for the time > being, borrow some pages). I am really confused now. The memcg reclaim cannot really reclaim anything from outside of the reclaimed hierarchy. Protected memcgs are only considered if the reclaim was not able to reclaim anything during the first hierarchy walk. That would imply that the reclaimed hierarchy has either all memcgs with memory protected or non-protected memcgs do not have any memory to reclaim. I think it would really help to provide much details about what is going on here before we can move forward. > > Why both B and C have low limit setup and they both cannot be reclaimed? > > Isn't that a weird setup where A hard limit is too close to sum of low > > limits of B and C? > > > > In other words could you share a more detailed configuration you are > > using and some more details why both B and C have been skipped during > > the first pass of the reclaim? > My practical scenario is that important processes(vip APP etc) are > placed into protected memcg and keep other processes just under root. > Current introduces direct reclaim because of alloc_pages(DMA_ALLOC > etc), in which the number of allocation would be much larger than low > but would NOT be charged to LRU. Whereas, current also wants to keep > the pages(.so files to exec) on LRU. I am sorry but this description makes even less sense to me. If your important process runs under a protected memcg and everything else is running under root memcg then your memcg will get protected as long as there is a reclaimable memory. There should ever be only global memory reclaim happening, unless you specify a hard/high limit on your important memcg. If you do so then there is no way to reclaim from outside of that specific memcg. I really fail how your patch can help with either of those situations.
On Tue, Oct 19, 2021 at 5:09 PM Michal Hocko <mhocko@suse.com> wrote: > > On Tue 19-10-21 15:11:30, Zhaoyang Huang wrote: > > On Mon, Oct 18, 2021 at 8:41 PM Michal Hocko <mhocko@suse.com> wrote: > > > > > > On Mon 18-10-21 17:25:23, Zhaoyang Huang wrote: > > > > On Mon, Oct 18, 2021 at 4:23 PM Michal Hocko <mhocko@suse.com> wrote: > [...] > > > > > I would be really curious about more specifics of the used hierarchy. > > > > What I am facing is a typical scenario on Android, that is a big > > > > memory consuming APP(camera etc) launched while background filled by > > > > other processes. The hierarchy is like what you describe above where B > > > > represents the APP and memory.low is set to help warm restart. Both of > > > > kswapd and direct reclaim work together to reclaim pages under this > > > > scenario, which can cause 20MB file page delete from LRU in several > > > > second. This change could help to have current process's page escape > > > > from being reclaimed and cause page thrashing. We observed the result > > > > via systrace which shows that the Uninterruptible sleep(block on page > > > > bit) and iowait get smaller than usual. > > > > > > I still have hard time to understand the exact setup and why the patch > > > helps you. If you want to protect B more than the low limit would allow > > > for by stealiong from C then the same thing can happen from anybody > > > reclaiming from C so in the end there is no protection. The same would > > > apply for any global direct memory reclaim done by a 3rd party. So I > > > suspect that your patch just happens to work by a luck. > > B and C compete fairly and superior than others. The idea based on > > assuming NOT all groups will trap into direct reclaim concurrently, so > > we want to have the groups steal pages from the processes under > > root(Non-memory sensitive) or other groups with lower thresholds(high > > memory tolerance) or the one totally sleeping(not busy for the time > > being, borrow some pages). > > I am really confused now. The memcg reclaim cannot really reclaim > anything from outside of the reclaimed hierarchy. Protected memcgs are > only considered if the reclaim was not able to reclaim anything during > the first hierarchy walk. That would imply that the reclaimed hierarchy > has either all memcgs with memory protected or non-protected memcgs do > not have any memory to reclaim. > > I think it would really help to provide much details about what is going > on here before we can move forward. > > > > Why both B and C have low limit setup and they both cannot be reclaimed? > > > Isn't that a weird setup where A hard limit is too close to sum of low > > > limits of B and C? > > > > > > In other words could you share a more detailed configuration you are > > > using and some more details why both B and C have been skipped during > > > the first pass of the reclaim? > > My practical scenario is that important processes(vip APP etc) are > > placed into protected memcg and keep other processes just under root. > > Current introduces direct reclaim because of alloc_pages(DMA_ALLOC > > etc), in which the number of allocation would be much larger than low > > but would NOT be charged to LRU. Whereas, current also wants to keep > > the pages(.so files to exec) on LRU. > > I am sorry but this description makes even less sense to me. If your > important process runs under a protected memcg and everything else is > running under root memcg then your memcg will get protected as long as > there is a reclaimable memory. There should ever be only global memory > reclaim happening, unless you specify a hard/high limit on your > important memcg. If you do so then there is no way to reclaim from > outside of that specific memcg. > > I really fail how your patch can help with either of those situations. please find cgv2 hierarchy on my sys[1], where uid_2000 is a cgroup under root and trace_printk info[3] from trace_printk embedded in shrink_node[2]. I don't why you say there should be no reclaim from groups under root which opposite to[3] [1] /sys/fs/cgroup # ls uid_2000 cgroup.controllers cgroup.max.depth cgroup.stat cgroup.type io.pressure memory.events.local memory.max memory.pressure memory.swap.events cgroup.events cgroup.max.descendants cgroup.subtree_control cpu.pressure memory.current memory.high memory.min memory.stat memory.swap.max cgroup.freeze cgroup.procs cgroup.threads cpu.stat memory.events memory.low memory.oom.group memory.swap.current pid_275 [2] @@ -2962,6 +2962,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) reclaimed = sc->nr_reclaimed; scanned = sc->nr_scanned; + trace_printk("root %x memcg %x reclaimed %ld\n",root_mem_cgroup,memcg,sc->nr_reclaimed); shrink_node_memcg(pgdat, memcg, sc, &lru_pages); node_lru_pages += lru_pages; [3] allocator@4.0-s-1034 [005] .... 442.077013: shrink_node: root ef022800 memcg ef027800 reclaimed 41 kworker/u16:3-931 [002] .... 442.077019: shrink_node: root ef022800 memcg c7e54000 reclaimed 17 allocator@4.0-s-1034 [005] .... 442.077019: shrink_node: root ef022800 memcg ef025000 reclaimed 41 allocator@4.0-s-1034 [005] .... 442.077024: shrink_node: root ef022800 memcg ef023000 reclaimed 41 kworker/u16:3-931 [002] .... 442.077026: shrink_node: root ef022800 memcg c7e57800 reclaimed 17 allocator@4.0-s-1034 [005] .... 442.077028: shrink_node: root ef022800 memcg ef026800 reclaimed 41 > -- > Michal Hocko > SUSE Labs
On Tue 19-10-21 20:17:16, Zhaoyang Huang wrote: > On Tue, Oct 19, 2021 at 5:09 PM Michal Hocko <mhocko@suse.com> wrote: > > > > On Tue 19-10-21 15:11:30, Zhaoyang Huang wrote: > > > On Mon, Oct 18, 2021 at 8:41 PM Michal Hocko <mhocko@suse.com> wrote: > > > > > > > > On Mon 18-10-21 17:25:23, Zhaoyang Huang wrote: > > > > > On Mon, Oct 18, 2021 at 4:23 PM Michal Hocko <mhocko@suse.com> wrote: > > [...] > > > > > > I would be really curious about more specifics of the used hierarchy. > > > > > What I am facing is a typical scenario on Android, that is a big > > > > > memory consuming APP(camera etc) launched while background filled by > > > > > other processes. The hierarchy is like what you describe above where B > > > > > represents the APP and memory.low is set to help warm restart. Both of > > > > > kswapd and direct reclaim work together to reclaim pages under this > > > > > scenario, which can cause 20MB file page delete from LRU in several > > > > > second. This change could help to have current process's page escape > > > > > from being reclaimed and cause page thrashing. We observed the result > > > > > via systrace which shows that the Uninterruptible sleep(block on page > > > > > bit) and iowait get smaller than usual. > > > > > > > > I still have hard time to understand the exact setup and why the patch > > > > helps you. If you want to protect B more than the low limit would allow > > > > for by stealiong from C then the same thing can happen from anybody > > > > reclaiming from C so in the end there is no protection. The same would > > > > apply for any global direct memory reclaim done by a 3rd party. So I > > > > suspect that your patch just happens to work by a luck. > > > B and C compete fairly and superior than others. The idea based on > > > assuming NOT all groups will trap into direct reclaim concurrently, so > > > we want to have the groups steal pages from the processes under > > > root(Non-memory sensitive) or other groups with lower thresholds(high > > > memory tolerance) or the one totally sleeping(not busy for the time > > > being, borrow some pages). > > > > I am really confused now. The memcg reclaim cannot really reclaim > > anything from outside of the reclaimed hierarchy. Protected memcgs are > > only considered if the reclaim was not able to reclaim anything during > > the first hierarchy walk. That would imply that the reclaimed hierarchy > > has either all memcgs with memory protected or non-protected memcgs do > > not have any memory to reclaim. > > > > I think it would really help to provide much details about what is going > > on here before we can move forward. > > > > > > Why both B and C have low limit setup and they both cannot be reclaimed? > > > > Isn't that a weird setup where A hard limit is too close to sum of low > > > > limits of B and C? > > > > > > > > In other words could you share a more detailed configuration you are > > > > using and some more details why both B and C have been skipped during > > > > the first pass of the reclaim? > > > My practical scenario is that important processes(vip APP etc) are > > > placed into protected memcg and keep other processes just under root. > > > Current introduces direct reclaim because of alloc_pages(DMA_ALLOC > > > etc), in which the number of allocation would be much larger than low > > > but would NOT be charged to LRU. Whereas, current also wants to keep > > > the pages(.so files to exec) on LRU. > > > > I am sorry but this description makes even less sense to me. If your > > important process runs under a protected memcg and everything else is > > running under root memcg then your memcg will get protected as long as > > there is a reclaimable memory. There should ever be only global memory > > reclaim happening, unless you specify a hard/high limit on your > > important memcg. If you do so then there is no way to reclaim from > > outside of that specific memcg. > > > > I really fail how your patch can help with either of those situations. > > please find cgv2 hierarchy on my sys[1], where uid_2000 is a cgroup > under root and trace_printk info[3] from trace_printk embedded in > shrink_node[2]. I don't why you say there should be no reclaim from > groups under root which opposite to[3] That is not what I am saying. I am saying the protected (by low limit) memcgs only get reclaimed if there is no reclaim progress from the reclaimed hierarchy. In your case that would mean that there is no reclaim from the root cgroup. > [1] > /sys/fs/cgroup # ls uid_2000 > cgroup.controllers cgroup.max.depth cgroup.stat > cgroup.type io.pressure memory.events.local memory.max > memory.pressure memory.swap.events > cgroup.events cgroup.max.descendants cgroup.subtree_control > cpu.pressure memory.current memory.high memory.min > memory.stat memory.swap.max > cgroup.freeze cgroup.procs cgroup.threads > cpu.stat memory.events memory.low memory.oom.group > memory.swap.current pid_275 This doesn't really help to make a better picture because it doesn't tell the configuration. It would help to print all cgroups with memory controller enabled and print memory.* values. > [2] > @@ -2962,6 +2962,7 @@ static bool shrink_node(pg_data_t *pgdat, struct > scan_control *sc) > > reclaimed = sc->nr_reclaimed; > scanned = sc->nr_scanned; > + trace_printk("root %x memcg %x reclaimed > %ld\n",root_mem_cgroup,memcg,sc->nr_reclaimed); > shrink_node_memcg(pgdat, memcg, sc, &lru_pages); > node_lru_pages += lru_pages; > > [3] > allocator@4.0-s-1034 [005] .... 442.077013: shrink_node: root > ef022800 memcg ef027800 reclaimed 41 > kworker/u16:3-931 [002] .... 442.077019: shrink_node: root > ef022800 memcg c7e54000 reclaimed 17 > allocator@4.0-s-1034 [005] .... 442.077019: shrink_node: root > ef022800 memcg ef025000 reclaimed 41 > allocator@4.0-s-1034 [005] .... 442.077024: shrink_node: root > ef022800 memcg ef023000 reclaimed 41 > kworker/u16:3-931 [002] .... 442.077026: shrink_node: root > ef022800 memcg c7e57800 reclaimed 17 > allocator@4.0-s-1034 [005] .... 442.077028: shrink_node: root > ef022800 memcg ef026800 reclaimed 41 It is impossible to tell which memcgs those are. It also doesn't tell anything whether low limit has been broken due to lack of progress.
On Tue, Oct 19, 2021 at 9:24 PM Michal Hocko <mhocko@suse.com> wrote: > > On Tue 19-10-21 20:17:16, Zhaoyang Huang wrote: > > On Tue, Oct 19, 2021 at 5:09 PM Michal Hocko <mhocko@suse.com> wrote: > > > > > > On Tue 19-10-21 15:11:30, Zhaoyang Huang wrote: > > > > On Mon, Oct 18, 2021 at 8:41 PM Michal Hocko <mhocko@suse.com> wrote: > > > > > > > > > > On Mon 18-10-21 17:25:23, Zhaoyang Huang wrote: > > > > > > On Mon, Oct 18, 2021 at 4:23 PM Michal Hocko <mhocko@suse.com> wrote: > > > [...] > > > > > > > I would be really curious about more specifics of the used hierarchy. > > > > > > What I am facing is a typical scenario on Android, that is a big > > > > > > memory consuming APP(camera etc) launched while background filled by > > > > > > other processes. The hierarchy is like what you describe above where B > > > > > > represents the APP and memory.low is set to help warm restart. Both of > > > > > > kswapd and direct reclaim work together to reclaim pages under this > > > > > > scenario, which can cause 20MB file page delete from LRU in several > > > > > > second. This change could help to have current process's page escape > > > > > > from being reclaimed and cause page thrashing. We observed the result > > > > > > via systrace which shows that the Uninterruptible sleep(block on page > > > > > > bit) and iowait get smaller than usual. > > > > > > > > > > I still have hard time to understand the exact setup and why the patch > > > > > helps you. If you want to protect B more than the low limit would allow > > > > > for by stealiong from C then the same thing can happen from anybody > > > > > reclaiming from C so in the end there is no protection. The same would > > > > > apply for any global direct memory reclaim done by a 3rd party. So I > > > > > suspect that your patch just happens to work by a luck. > > > > B and C compete fairly and superior than others. The idea based on > > > > assuming NOT all groups will trap into direct reclaim concurrently, so > > > > we want to have the groups steal pages from the processes under > > > > root(Non-memory sensitive) or other groups with lower thresholds(high > > > > memory tolerance) or the one totally sleeping(not busy for the time > > > > being, borrow some pages). > > > > > > I am really confused now. The memcg reclaim cannot really reclaim > > > anything from outside of the reclaimed hierarchy. Protected memcgs are > > > only considered if the reclaim was not able to reclaim anything during > > > the first hierarchy walk. That would imply that the reclaimed hierarchy > > > has either all memcgs with memory protected or non-protected memcgs do > > > not have any memory to reclaim. > > > > > > I think it would really help to provide much details about what is going > > > on here before we can move forward. > > > > > > > > Why both B and C have low limit setup and they both cannot be reclaimed? > > > > > Isn't that a weird setup where A hard limit is too close to sum of low > > > > > limits of B and C? > > > > > > > > > > In other words could you share a more detailed configuration you are > > > > > using and some more details why both B and C have been skipped during > > > > > the first pass of the reclaim? > > > > My practical scenario is that important processes(vip APP etc) are > > > > placed into protected memcg and keep other processes just under root. > > > > Current introduces direct reclaim because of alloc_pages(DMA_ALLOC > > > > etc), in which the number of allocation would be much larger than low > > > > but would NOT be charged to LRU. Whereas, current also wants to keep > > > > the pages(.so files to exec) on LRU. > > > > > > I am sorry but this description makes even less sense to me. If your > > > important process runs under a protected memcg and everything else is > > > running under root memcg then your memcg will get protected as long as > > > there is a reclaimable memory. There should ever be only global memory > > > reclaim happening, unless you specify a hard/high limit on your > > > important memcg. If you do so then there is no way to reclaim from > > > outside of that specific memcg. > > > > > > I really fail how your patch can help with either of those situations. > > > > please find cgv2 hierarchy on my sys[1], where uid_2000 is a cgroup > > under root and trace_printk info[3] from trace_printk embedded in > > shrink_node[2]. I don't why you say there should be no reclaim from > > groups under root which opposite to[3] > > That is not what I am saying. I am saying the protected (by low limit) > memcgs only get reclaimed if there is no reclaim progress from the > reclaimed hierarchy. In your case that would mean that there is no > reclaim from the root cgroup. Do you mean that direct reclaim should succeed for the first round reclaim within which memcg get protected by memory.low and would NOT retry by setting memcg_low_reclaim to true? It is not true in android like system, where reclaim always failed and introduce lmk and even OOM. > > > [1] > > /sys/fs/cgroup # ls uid_2000 > > cgroup.controllers cgroup.max.depth cgroup.stat > > cgroup.type io.pressure memory.events.local memory.max > > memory.pressure memory.swap.events > > cgroup.events cgroup.max.descendants cgroup.subtree_control > > cpu.pressure memory.current memory.high memory.min > > memory.stat memory.swap.max > > cgroup.freeze cgroup.procs cgroup.threads > > cpu.stat memory.events memory.low memory.oom.group > > memory.swap.current pid_275 > > This doesn't really help to make a better picture because it doesn't > tell the configuration. It would help to print all cgroups with memory > controller enabled and print memory.* values. > > > [2] > > @@ -2962,6 +2962,7 @@ static bool shrink_node(pg_data_t *pgdat, struct > > scan_control *sc) > > > > reclaimed = sc->nr_reclaimed; > > scanned = sc->nr_scanned; > > + trace_printk("root %x memcg %x reclaimed > > %ld\n",root_mem_cgroup,memcg,sc->nr_reclaimed); > > shrink_node_memcg(pgdat, memcg, sc, &lru_pages); > > node_lru_pages += lru_pages; > > > > [3] > > allocator@4.0-s-1034 [005] .... 442.077013: shrink_node: root > > ef022800 memcg ef027800 reclaimed 41 > > kworker/u16:3-931 [002] .... 442.077019: shrink_node: root > > ef022800 memcg c7e54000 reclaimed 17 > > allocator@4.0-s-1034 [005] .... 442.077019: shrink_node: root > > ef022800 memcg ef025000 reclaimed 41 > > allocator@4.0-s-1034 [005] .... 442.077024: shrink_node: root > > ef022800 memcg ef023000 reclaimed 41 > > kworker/u16:3-931 [002] .... 442.077026: shrink_node: root > > ef022800 memcg c7e57800 reclaimed 17 > > allocator@4.0-s-1034 [005] .... 442.077028: shrink_node: root > > ef022800 memcg ef026800 reclaimed 41 > > It is impossible to tell which memcgs those are. It also doesn't tell > anything whether low limit has been broken due to lack of progress. > -- > Michal Hocko > SUSE Labs
On Wed 20-10-21 15:33:39, Zhaoyang Huang wrote: [...] > Do you mean that direct reclaim should succeed for the first round > reclaim within which memcg get protected by memory.low and would NOT > retry by setting memcg_low_reclaim to true? Yes, this is the semantic of low limit protection in the upstream kernel. Have a look at do_try_to_free_pages and how it sets memcg_low_reclaim only if there were no pages reclaimed. > It is not true in android > like system, where reclaim always failed and introduce lmk and even > OOM. I am not familiar with android specific changes to the upstream reclaim logic. You should be investigating why the reclaim couldn't make a forward progress (aka reclaim pages) from non-protected memcgs. There are tracepoints you can use (generally vmscan prefix).
On Wed, Oct 20, 2021 at 4:55 PM Michal Hocko <mhocko@suse.com> wrote: > > On Wed 20-10-21 15:33:39, Zhaoyang Huang wrote: > [...] > > Do you mean that direct reclaim should succeed for the first round > > reclaim within which memcg get protected by memory.low and would NOT > > retry by setting memcg_low_reclaim to true? > > Yes, this is the semantic of low limit protection in the upstream > kernel. Have a look at do_try_to_free_pages and how it sets > memcg_low_reclaim only if there were no pages reclaimed. > > > It is not true in android > > like system, where reclaim always failed and introduce lmk and even > > OOM. > > I am not familiar with android specific changes to the upstream reclaim > logic. You should be investigating why the reclaim couldn't make a > forward progress (aka reclaim pages) from non-protected memcgs. There > are tracepoints you can use (generally vmscan prefix). Ok, I am aware of why you get confused now. I think you are analysing cgroup's behaviour according to a pre-defined workload and memory pattern, which should work according to the design, such as processes within root should provide memory before protected memcg get reclaimed. You can refer [1] as the hierarchy, where effective userspace workloads locate in protect groups and have rest of processes be non-grouped. In fact, non-grouped ones can not provide enough memory as they are kernel threads and the processes with few pages on LRU(control logic inside). The practical scenario is groupA launched a high-order kmalloc and introduce reclaiming(kswapd and direct reclaim). As I said, non-grouped ones can not provide enough contiguous memory blocks which let direct reclaim quickly fail for the first round reclaiming. What I am trying to do is that let kswapd try more for the target. It is also fair if groupA,B,C are trapping in slow path concurrently. [1] root | | | | non-grouped processes groupA groupB groupC > > -- > Michal Hocko > SUSE Labs
On Wed 20-10-21 19:45:33, Zhaoyang Huang wrote: > On Wed, Oct 20, 2021 at 4:55 PM Michal Hocko <mhocko@suse.com> wrote: > > > > On Wed 20-10-21 15:33:39, Zhaoyang Huang wrote: > > [...] > > > Do you mean that direct reclaim should succeed for the first round > > > reclaim within which memcg get protected by memory.low and would NOT > > > retry by setting memcg_low_reclaim to true? > > > > Yes, this is the semantic of low limit protection in the upstream > > kernel. Have a look at do_try_to_free_pages and how it sets > > memcg_low_reclaim only if there were no pages reclaimed. > > > > > It is not true in android > > > like system, where reclaim always failed and introduce lmk and even > > > OOM. > > > > I am not familiar with android specific changes to the upstream reclaim > > logic. You should be investigating why the reclaim couldn't make a > > forward progress (aka reclaim pages) from non-protected memcgs. There > > are tracepoints you can use (generally vmscan prefix). > Ok, I am aware of why you get confused now. I think you are analysing > cgroup's behaviour according to a pre-defined workload and memory > pattern, which should work according to the design, such as processes > within root should provide memory before protected memcg get > reclaimed. You can refer [1] as the hierarchy, where effective > userspace workloads locate in protect groups and have rest of > processes be non-grouped. In fact, non-grouped ones can not provide > enough memory as they are kernel threads and the processes with few > pages on LRU(control logic inside). The practical scenario is groupA > launched a high-order kmalloc and introduce reclaiming(kswapd and > direct reclaim). As I said, non-grouped ones can not provide enough > contiguous memory blocks which let direct reclaim quickly fail for the > first round reclaiming. What I am trying to do is that let kswapd try > more for the target. It is also fair if groupA,B,C are trapping in > slow path concurrently. > > [1] > root > | | > | | > non-grouped processes groupA groupB groupC I am sorry but I still do not understand your setup. I have asked several times for more specifics. Without that I cannot really wrap my head around your (ever changing) statements. This is not really a productive use of time. I am sorry but I cannot really help you much without understanding the actual problem.
diff --git a/mm/vmscan.c b/mm/vmscan.c index 5199b96..ebbdc37 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) sc->memcg_low_skipped = 1; continue; } + /* + * Don't bother current when its memcg is below low + */ + if (get_mem_cgroup_from_mm(current->mm) == memcg) + continue; memcg_memory_event(memcg, MEMCG_LOW); }
From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> Sibling thread of the same process could refault the reclaimed pages in the same time, which would be typical in None global reclaim and introduce thrashing. --- mm/vmscan.c | 5 +++++ 1 file changed, 5 insertions(+)