On Mon, 18 Oct 2010 17:39:35 -0700 Greg Thelen <gthelen@xxxxxxxxxx> wrote: > Document cgroup dirty memory interfaces and statistics. > > Signed-off-by: Andrea Righi <arighi@xxxxxxxxxxx> > Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx> > --- > > 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 | 60 ++++++++++++++++++++++++++++++++++++++ > 1 files changed, 60 insertions(+), 0 deletions(-) > > diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt > index 7781857..02bbd6f 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 Shouldn't we add description of "total_diryt/writeback/nfs_unstable" too ? Seeing [5/11], it will be showed in memory.stat. > @@ -453,6 +457,62 @@ 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. > + > 6. Hierarchy support > > The memory controller supports a deep hierarchy and hierarchical accounting. > -- > 1.7.1 > Can you clarify whether we can limit the "total" dirty pages under hierarchy in use_hierarchy==1 case ? If we can, I think it would be better to note it in this documentation. Thanks, Daisuke Nishimura. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>