Document cgroup dirty memory interfaces and statistics. Signed-off-by: Andrea Righi <arighi@xxxxxxxxxxx> Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Acked-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> --- Changelog since v4: - Minor rewording of '5.5 dirty memory' section. - Added '5.5.1 Inode writeback issue' section. 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 | 80 ++++++++++++++++++++++++++++++++++++++ 1 files changed, 80 insertions(+), 0 deletions(-) diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index b6ed61c..4db695e 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 +460,79 @@ 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 throttled if they cross that limit. System-wide dirty limits are also +consulted. Dirty memory consumption is checked against both system-wide and +per-cgroup dirty limits. + +The interface is similar to the procfs interface: /proc/sys/vm/dirty_*. It is +possible to configure a limit to trigger throttling of a dirtier or queue +background writeback. 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 be throttled. + The default value is the system-wide dirty ratio, /proc/sys/vm/dirty_ratio. + +- memory.dirty_limit_in_bytes: the amount of dirty memory (expressed in bytes) + in the cgroup at which a process generating dirty pages will be throttled. + Suffix (k, K, m, M, g, or G) can be used to indicate that value is kilo, mega + or gigabytes. The default value is the system-wide dirty limit, + /proc/sys/vm/dirty_bytes. + + Note: memory.dirty_limit_in_bytes is the counterpart of memory.dirty_ratio. + Only one 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. The default value is the + system-wide background dirty ratio, /proc/sys/vm/dirty_background_ratio. + +- 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. The default value is the + system-wide dirty background limit, /proc/sys/vm/dirty_background_bytes. + + Note: memory.dirty_background_limit_in_bytes is the counterpart of + memory.dirty_background_ratio. Only one 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 independent dirty memory usage and limits. +When use_hierarchy=1 the dirty limits of parents cgroups are also checked to +ensure that no dirty limit is exceeded. + +5.5.1 Inode writeback issue + +When a memcg dirty limit is exceeded, then bdi writeback is employed to +writeback dirty inodes. Bdi writeback considers inodes from any memcg, not just +inodes contributing dirty pages to the memcg exceeding its limit. Ideally when +a memcg dirty limit is exceeded only inodes contributing dirty pages to that +memcg would be considered for writeback. However, the current implementation +does not behave this way because there is no way to quickly check the memcgs +that an inode contributes dirty pages to. + 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-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
