| Message ID | 1546647560-40026-3-git-send-email-yang.shi@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: memcontrol: do memory reclaim when offlining | expand |
On Fri, Jan 4, 2019 at 4:21 PM Yang Shi <yang.shi@linux.alibaba.com> wrote: > > The typical usecase of force empty is to try to reclaim as much as > possible memory before offlining a memcg. Since there should be no > attached tasks to offlining memcg, the tasks anonymous pages would have > already been freed or uncharged. Even though anonymous pages get > swapped out, but they still get charged to swap space. So, it sounds > pointless to do swap for force empty. > > I tried to dig into the history of this, it was introduced by > commit 8c7c6e34a125 ("memcg: mem+swap controller core"), but there is > not any clue about why it was done so at the first place. > > The below simple test script shows slight file cache reclaim improvement > when swap is on. > > echo 3 > /proc/sys/vm/drop_caches > mkdir /sys/fs/cgroup/memory/test > echo 30 > /sys/fs/cgroup/memory/test/memory.swappiness > echo $$ >/sys/fs/cgroup/memory/test/cgroup.procs > cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' > dd if=/dev/zero of=/mnt/test bs=1M count=1024 > ping localhost > /dev/null & > echo 1 > /sys/fs/cgroup/memory/test/memory.force_empty > killall ping > echo $$ >/sys/fs/cgroup/memory/cgroup.procs > cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' > rmdir /sys/fs/cgroup/memory/test > cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' > > The number of page cache is: > w/o w/ > before force empty 1088792 1088784 > after force empty 41492 39428 > reclaimed 1047300 1049356 > > Without doing swap, force empty can reclaim 2MB more memory in 1GB page > cache. > > Cc: Michal Hocko <mhocko@suse.com> > Cc: Johannes Weiner <hannes@cmpxchg.org> > Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> > --- > mm/memcontrol.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index af7f18b..75208a2 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2895,7 +2895,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg) > return -EINTR; > > progress = try_to_free_mem_cgroup_pages(memcg, 1, > - GFP_KERNEL, true); > + GFP_KERNEL, false); I think we agreed not to change the behavior of force_empty. You can customize 'force_empty on wipe_on_offline' to not swapout. > if (!progress) { > nr_retries--; > /* maybe some writeback is necessary */ > -- > 1.8.3.1 >
On 1/4/19 4:43 PM, Shakeel Butt wrote: > On Fri, Jan 4, 2019 at 4:21 PM Yang Shi <yang.shi@linux.alibaba.com> wrote: >> The typical usecase of force empty is to try to reclaim as much as >> possible memory before offlining a memcg. Since there should be no >> attached tasks to offlining memcg, the tasks anonymous pages would have >> already been freed or uncharged. Even though anonymous pages get >> swapped out, but they still get charged to swap space. So, it sounds >> pointless to do swap for force empty. >> >> I tried to dig into the history of this, it was introduced by >> commit 8c7c6e34a125 ("memcg: mem+swap controller core"), but there is >> not any clue about why it was done so at the first place. >> >> The below simple test script shows slight file cache reclaim improvement >> when swap is on. >> >> echo 3 > /proc/sys/vm/drop_caches >> mkdir /sys/fs/cgroup/memory/test >> echo 30 > /sys/fs/cgroup/memory/test/memory.swappiness >> echo $$ >/sys/fs/cgroup/memory/test/cgroup.procs >> cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' >> dd if=/dev/zero of=/mnt/test bs=1M count=1024 >> ping localhost > /dev/null & >> echo 1 > /sys/fs/cgroup/memory/test/memory.force_empty >> killall ping >> echo $$ >/sys/fs/cgroup/memory/cgroup.procs >> cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' >> rmdir /sys/fs/cgroup/memory/test >> cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' >> >> The number of page cache is: >> w/o w/ >> before force empty 1088792 1088784 >> after force empty 41492 39428 >> reclaimed 1047300 1049356 >> >> Without doing swap, force empty can reclaim 2MB more memory in 1GB page >> cache. >> >> Cc: Michal Hocko <mhocko@suse.com> >> Cc: Johannes Weiner <hannes@cmpxchg.org> >> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> >> --- >> mm/memcontrol.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index af7f18b..75208a2 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -2895,7 +2895,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg) >> return -EINTR; >> >> progress = try_to_free_mem_cgroup_pages(memcg, 1, >> - GFP_KERNEL, true); >> + GFP_KERNEL, false); > I think we agreed not to change the behavior of force_empty. You can > customize 'force_empty on wipe_on_offline' to not swapout. OK, will keep force_empty intact. Thanks, Yang > >> if (!progress) { >> nr_retries--; >> /* maybe some writeback is necessary */ >> -- >> 1.8.3.1 >>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index af7f18b..75208a2 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2895,7 +2895,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg) return -EINTR; progress = try_to_free_mem_cgroup_pages(memcg, 1, - GFP_KERNEL, true); + GFP_KERNEL, false); if (!progress) { nr_retries--; /* maybe some writeback is necessary */
The typical usecase of force empty is to try to reclaim as much as possible memory before offlining a memcg. Since there should be no attached tasks to offlining memcg, the tasks anonymous pages would have already been freed or uncharged. Even though anonymous pages get swapped out, but they still get charged to swap space. So, it sounds pointless to do swap for force empty. I tried to dig into the history of this, it was introduced by commit 8c7c6e34a125 ("memcg: mem+swap controller core"), but there is not any clue about why it was done so at the first place. The below simple test script shows slight file cache reclaim improvement when swap is on. echo 3 > /proc/sys/vm/drop_caches mkdir /sys/fs/cgroup/memory/test echo 30 > /sys/fs/cgroup/memory/test/memory.swappiness echo $$ >/sys/fs/cgroup/memory/test/cgroup.procs cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' dd if=/dev/zero of=/mnt/test bs=1M count=1024 ping localhost > /dev/null & echo 1 > /sys/fs/cgroup/memory/test/memory.force_empty killall ping echo $$ >/sys/fs/cgroup/memory/cgroup.procs cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' rmdir /sys/fs/cgroup/memory/test cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' The number of page cache is: w/o w/ before force empty 1088792 1088784 after force empty 41492 39428 reclaimed 1047300 1049356 Without doing swap, force empty can reclaim 2MB more memory in 1GB page cache. Cc: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> --- mm/memcontrol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)