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Message-Id: <1288336154-23256-3-git-send-email-gthelen@google.com> Date: Fri, 29 Oct 2010 00:09:05 -0700 From: Greg Thelen <gthelen@...gle.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, containers@...ts.osdl.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>, Ciju Rajan K <ciju@...ux.vnet.ibm.com>, David Rientjes <rientjes@...gle.com>, Wu Fengguang <fengguang.wu@...el.com>, Greg Thelen <gthelen@...gle.com> Subject: [PATCH v4 02/11] memcg: document cgroup dirty memory interfaces Document cgroup dirty memory interfaces and statistics. Signed-off-by: Andrea Righi <arighi@...eler.com> Signed-off-by: Greg Thelen <gthelen@...gle.com> --- Changelog since v3: - Described interactions with memory.use_hierarchy. - Added description of total_dirty, total_writeback, and total_nfs_unstable. Changelog since v1: - Renamed "nfs"/"total_nfs" to "nfs_unstable"/"total_nfs_unstable" in per cgroup memory.stat to match /proc/meminfo. - Allow [kKmMgG] suffixes for newly created dirty limit value cgroupfs files. - Describe a situation where a cgroup can exceed its dirty limit. Documentation/cgroups/memory.txt | 73 ++++++++++++++++++++++++++++++++++++++ 1 files changed, 73 insertions(+), 0 deletions(-) diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index 7781857..a3861f3 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -385,6 +385,10 @@ mapped_file - # of bytes of mapped file (includes tmpfs/shmem) pgpgin - # of pages paged in (equivalent to # of charging events). pgpgout - # of pages paged out (equivalent to # of uncharging events). swap - # of bytes of swap usage +dirty - # of bytes that are waiting to get written back to the disk. +writeback - # of bytes that are actively being written back to the disk. +nfs_unstable - # of bytes sent to the NFS server, but not yet committed to + the actual storage. inactive_anon - # of bytes of anonymous memory and swap cache memory on LRU list. active_anon - # of bytes of anonymous and swap cache memory on active @@ -406,6 +410,9 @@ total_mapped_file - sum of all children's "cache" total_pgpgin - sum of all children's "pgpgin" total_pgpgout - sum of all children's "pgpgout" total_swap - sum of all children's "swap" +total_dirty - sum of all children's "dirty" +total_writeback - sum of all children's "writeback" +total_nfs_unstable - sum of all children's "nfs_unstable" total_inactive_anon - sum of all children's "inactive_anon" total_active_anon - sum of all children's "active_anon" total_inactive_file - sum of all children's "inactive_file" @@ -453,6 +460,72 @@ memory under it will be reclaimed. You can reset failcnt by writing 0 to failcnt file. # echo 0 > .../memory.failcnt +5.5 dirty memory + +Control the maximum amount of dirty pages a cgroup can have at any given time. + +Limiting dirty memory is like fixing the max amount of dirty (hard to reclaim) +page cache used by a cgroup. So, in case of multiple cgroup writers, they will +not be able to consume more than their designated share of dirty pages and will +be forced to perform write-out if they cross that limit. + +The interface is equivalent to the procfs interface: /proc/sys/vm/dirty_*. It +is possible to configure a limit to trigger both a direct writeback or a +background writeback performed by per-bdi flusher threads. The root cgroup +memory.dirty_* control files are read-only and match the contents of +the /proc/sys/vm/dirty_* files. + +Per-cgroup dirty limits can be set using the following files in the cgroupfs: + +- memory.dirty_ratio: the amount of dirty memory (expressed as a percentage of + cgroup memory) at which a process generating dirty pages will itself start + writing out dirty data. + +- memory.dirty_limit_in_bytes: the amount of dirty memory (expressed in bytes) + in the cgroup at which a process generating dirty pages will start itself + writing out dirty data. Suffix (k, K, m, M, g, or G) can be used to indicate + that value is kilo, mega or gigabytes. + + Note: memory.dirty_limit_in_bytes is the counterpart of memory.dirty_ratio. + Only one of them may be specified at a time. When one is written it is + immediately taken into account to evaluate the dirty memory limits and the + other appears as 0 when read. + +- memory.dirty_background_ratio: the amount of dirty memory of the cgroup + (expressed as a percentage of cgroup memory) at which background writeback + kernel threads will start writing out dirty data. + +- memory.dirty_background_limit_in_bytes: the amount of dirty memory (expressed + in bytes) in the cgroup at which background writeback kernel threads will + start writing out dirty data. Suffix (k, K, m, M, g, or G) can be used to + indicate that value is kilo, mega or gigabytes. + + Note: memory.dirty_background_limit_in_bytes is the counterpart of + memory.dirty_background_ratio. Only one of them may be specified at a time. + When one is written it is immediately taken into account to evaluate the dirty + memory limits and the other appears as 0 when read. + +A cgroup may contain more dirty memory than its dirty limit. This is possible +because of the principle that the first cgroup to touch a page is charged for +it. Subsequent page counting events (dirty, writeback, nfs_unstable) are also +counted to the originally charged cgroup. + +Example: If page is allocated by a cgroup A task, then the page is charged to +cgroup A. If the page is later dirtied by a task in cgroup B, then the cgroup A +dirty count will be incremented. If cgroup A is over its dirty limit but cgroup +B is not, then dirtying a cgroup A page from a cgroup B task may push cgroup A +over its dirty limit without throttling the dirtying cgroup B task. + +When use_hierarchy=0, each cgroup has dirty memory usage and limits. +System-wide dirty limits are also consulted. Dirty memory consumption is +checked against both system-wide and per-cgroup dirty limits. + +The current implementation does enforce per-cgroup dirty limits when +use_hierarchy=1. System-wide dirty limits are used for processes in such +cgroups. Attempts to read memory.dirty_* files return the system-wide values. +Writes to the memory.dirty_* files return error. An enhanced implementation is +needed to check the chain of parents to ensure that no dirty limit is exceeded. + 6. Hierarchy support The memory controller supports a deep hierarchy and hierarchical accounting. -- 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/
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