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Message-ID: <BANLkTik50YQtoLVHFg7BP6KLz7GtvU1KzEjdCwx620oYWBH0qQ@mail.gmail.com> Date: Fri, 3 Jun 2011 15:50:28 -0700 From: Greg Thelen <gthelen@...gle.com> To: Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, containers@...ts.osdl.org, linux-fsdevel@...r.kernel.org, Andrea Righi <arighi@...eler.com>, Balbir Singh <balbir@...ux.vnet.ibm.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Daisuke Nishimura <nishimura@....nes.nec.co.jp>, Minchan Kim <minchan.kim@...il.com>, Johannes Weiner <hannes@...xchg.org>, Ciju Rajan K <ciju@...ux.vnet.ibm.com>, David Rientjes <rientjes@...gle.com>, Wu Fengguang <fengguang.wu@...el.com>, Vivek Goyal <vgoyal@...hat.com>, Dave Chinner <david@...morbit.com> Subject: Re: [PATCH v8 00/12] memcg: per cgroup dirty page accounting On Fri, Jun 3, 2011 at 3:46 PM, Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com> wrote: > 2011/6/4 Greg Thelen <gthelen@...gle.com>: >> This patch series provides the ability for each cgroup to have independent dirty >> page usage limits. Limiting dirty memory fixes the max amount of dirty (hard to >> reclaim) page cache used by a cgroup. This allows for better per cgroup memory >> isolation and fewer ooms within a single cgroup. >> >> Having per cgroup dirty memory limits is not very interesting unless writeback >> is cgroup aware. There is not much isolation if cgroups have to writeback data >> from other cgroups to get below their dirty memory threshold. >> >> Per-memcg dirty limits are provided to support isolation and thus cross cgroup >> inode sharing is not a priority. This allows the code be simpler. >> >> To add cgroup awareness to writeback, this series adds a memcg field to the >> inode to allow writeback to isolate inodes for a particular cgroup. When an >> inode is marked dirty, i_memcg is set to the current cgroup. When inode pages >> are marked dirty the i_memcg field compared against the page's cgroup. If they >> differ, then the inode is marked as shared by setting i_memcg to a special >> shared value (zero). >> >> Previous discussions suggested that a per-bdi per-memcg b_dirty list was a good >> way to assoicate inodes with a cgroup without having to add a field to struct >> inode. I prototyped this approach but found that it involved more complex >> writeback changes and had at least one major shortcoming: detection of when an >> inode becomes shared by multiple cgroups. While such sharing is not expected to >> be common, the system should gracefully handle it. >> >> balance_dirty_pages() calls mem_cgroup_balance_dirty_pages(), which checks the >> dirty usage vs dirty thresholds for the current cgroup and its parents. If any >> over-limit cgroups are found, they are marked in a global over-limit bitmap >> (indexed by cgroup id) and the bdi flusher is awoke. >> >> The bdi flusher uses wb_check_background_flush() to check for any memcg over >> their dirty limit. When performing per-memcg background writeback, >> move_expired_inodes() walks per bdi b_dirty list using each inode's i_memcg and >> the global over-limit memcg bitmap to determine if the inode should be written. >> >> If mem_cgroup_balance_dirty_pages() is unable to get below the dirty page >> threshold writing per-memcg inodes, then downshifts to also writing shared >> inodes (i_memcg=0). >> >> I know that there is some significant writeback changes associated with the >> IO-less balance_dirty_pages() effort. I am not trying to derail that, so this >> patch series is merely an RFC to get feedback on the design. There are probably >> some subtle races in these patches. I have done moderate functional testing of >> the newly proposed features. >> > > Thank you...hmm, is this set really "merely RFC ?". I'd like to merge > this function > before other new big hammer works because this makes behavior of memcg > much better. Oops. I meant to remove the above RFC paragraph. This -v8 patch series is intended for merging into mmotm. > I'd like to review and test this set (but maybe I can't do much in the > weekend...) Thank you. > Anyway, thank you. > -Kame >> Here is an example of the memcg-oom that is avoided with this patch series: >> # mkdir /dev/cgroup/memory/x >> # echo 100M > /dev/cgroup/memory/x/memory.limit_in_bytes >> # echo $$ > /dev/cgroup/memory/x/tasks >> # dd if=/dev/zero of=/data/f1 bs=1k count=1M & >> # dd if=/dev/zero of=/data/f2 bs=1k count=1M & >> # wait >> [1]- Killed dd if=/dev/zero of=/data/f1 bs=1M count=1k >> [2]+ Killed dd if=/dev/zero of=/data/f1 bs=1M count=1k >> >> Known limitations: >> If a dirty limit is lowered a cgroup may be over its limit. >> >> Changes since -v7: >> - Merged -v7 09/14 'cgroup: move CSS_ID_MAX to cgroup.h' into >> -v8 09/13 'memcg: create support routines for writeback' >> >> - Merged -v7 08/14 'writeback: add memcg fields to writeback_control' >> into -v8 09/13 'memcg: create support routines for writeback' and >> -v8 10/13 'memcg: create support routines for page-writeback'. This >> moves the declaration of new fields with the first usage of the >> respective fields. >> >> - mem_cgroup_writeback_done() now clears corresponding bit for cgroup that >> cannot be referenced. Such a bit would represent a cgroup previously over >> dirty limit, but that has been deleted before writeback cleaned all pages. By >> clearing bit, writeback will not continually try to writeback the deleted >> cgroup. >> >> - Previously mem_cgroup_writeback_done() would only finish writeback when the >> cgroup's dirty memory usage dropped below the dirty limit. This was the wrong >> limit to check. This now correctly checks usage against the background dirty >> limit. >> >> - over_bground_thresh() now sets shared_inodes=1. In -v7 per memcg >> background writeback did not, so it did not write pages of shared >> inodes in background writeback. In the (potentially common) case >> where the system dirty memory usage is below the system background >> dirty threshold but at least one cgroup is over its background dirty >> limit, then per memcg background writeback is queued for any >> over-background-threshold cgroups. Background writeback should be >> allowed to writeback shared inodes. The hope is that writing such >> inodes has good chance of cleaning the inodes so they can transition >> from shared to non-shared. Such a transition is good because then the >> inode will remain unshared until it is written by multiple cgroup. >> Non-shared inodes offer better isolation. >> >> Single patch that can be applied to mmotm-2011-05-12-15-52: >> http://www.kernel.org/pub/linux/kernel/people/gthelen/memcg/memcg-dirty-limits-v8-on-mmotm-2011-05-12-15-52.patch >> >> Patches are based on mmotm-2011-05-12-15-52. >> >> Greg Thelen (12): >> memcg: document cgroup dirty memory interfaces >> memcg: add page_cgroup flags for dirty page tracking >> memcg: add mem_cgroup_mark_inode_dirty() >> memcg: add dirty page accounting infrastructure >> memcg: add kernel calls for memcg dirty page stats >> memcg: add dirty limits to mem_cgroup >> memcg: add cgroupfs interface to memcg dirty limits >> memcg: dirty page accounting support routines >> memcg: create support routines for writeback >> memcg: create support routines for page-writeback >> writeback: make background writeback cgroup aware >> memcg: check memcg dirty limits in page writeback >> >> Documentation/cgroups/memory.txt | 70 ++++ >> fs/fs-writeback.c | 34 ++- >> fs/inode.c | 3 + >> fs/nfs/write.c | 4 + >> include/linux/cgroup.h | 1 + >> include/linux/fs.h | 9 + >> include/linux/memcontrol.h | 63 ++++- >> include/linux/page_cgroup.h | 23 ++ >> include/linux/writeback.h | 5 +- >> include/trace/events/memcontrol.h | 198 +++++++++++ >> kernel/cgroup.c | 1 - >> mm/filemap.c | 1 + >> mm/memcontrol.c | 708 ++++++++++++++++++++++++++++++++++++- >> mm/page-writeback.c | 42 ++- >> mm/truncate.c | 1 + >> mm/vmscan.c | 2 +- >> 16 files changed, 1138 insertions(+), 27 deletions(-) >> create mode 100644 include/trace/events/memcontrol.h >> >> -- >> 1.7.3.1 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majordomo@...r.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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