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-rw-r--r--Documentation/cgroups/memory.txt37
1 files changed, 16 insertions, 21 deletions
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 9b1067a..dd88540 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -184,12 +184,14 @@ behind this approach is that a cgroup that aggressively uses a shared
page will eventually get charged for it (once it is uncharged from
the cgroup that brought it in -- this will happen on memory pressure).
+But see section 8.2: when moving a task to another cgroup, its pages may
+be recharged to the new cgroup, if move_charge_at_immigrate has been chosen.
+
Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used.
When you do swapoff and make swapped-out pages of shmem(tmpfs) to
be backed into memory in force, charges for pages are accounted against the
caller of swapoff rather than the users of shmem.
-
2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP)
Swap Extension allows you to record charge for swap. A swapped-in page is
@@ -374,14 +376,15 @@ cgroup might have some charge associated with it, even though all
tasks have migrated away from it. (because we charge against pages, not
against tasks.)
-Such charges are freed or moved to their parent. At moving, both of RSS
-and CACHES are moved to parent.
-rmdir() may return -EBUSY if freeing/moving fails. See 5.1 also.
+We move the stats to root (if use_hierarchy==0) or parent (if
+use_hierarchy==1), and no change on the charge except uncharging
+from the child.
Charges recorded in swap information is not updated at removal of cgroup.
Recorded information is discarded and a cgroup which uses swap (swapcache)
will be charged as a new owner of it.
+About use_hierarchy, see Section 6.
5. Misc. interfaces.
@@ -394,13 +397,15 @@ will be charged as a new owner of it.
Almost all pages tracked by this memory cgroup will be unmapped and freed.
Some pages cannot be freed because they are locked or in-use. Such pages are
- moved to parent and this cgroup will be empty. This may return -EBUSY if
- VM is too busy to free/move all pages immediately.
+ moved to parent(if use_hierarchy==1) or root (if use_hierarchy==0) and this
+ cgroup will be empty.
Typical use case of this interface is that calling this before rmdir().
Because rmdir() moves all pages to parent, some out-of-use page caches can be
moved to the parent. If you want to avoid that, force_empty will be useful.
+ About use_hierarchy, see Section 6.
+
5.2 stat file
memory.stat file includes following statistics
@@ -430,17 +435,10 @@ hierarchical_memory_limit - # of bytes of memory limit with regard to hierarchy
hierarchical_memsw_limit - # of bytes of memory+swap limit with regard to
hierarchy under which memory cgroup is.
-total_cache - sum of all children's "cache"
-total_rss - sum of all children's "rss"
-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_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"
-total_active_file - sum of all children's "active_file"
-total_unevictable - sum of all children's "unevictable"
+total_<counter> - # hierarchical version of <counter>, which in
+ addition to the cgroup's own value includes the
+ sum of all hierarchical children's values of
+ <counter>, i.e. total_cache
# The following additional stats are dependent on CONFIG_DEBUG_VM.
@@ -622,8 +620,7 @@ memory cgroup.
bit | what type of charges would be moved ?
-----+------------------------------------------------------------------------
0 | A charge of an anonymous page(or swap of it) used by the target task.
- | Those pages and swaps must be used only by the target task. You must
- | enable Swap Extension(see 2.4) to enable move of swap charges.
+ | You must enable Swap Extension(see 2.4) to enable move of swap charges.
-----+------------------------------------------------------------------------
1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory)
| and swaps of tmpfs file) mmapped by the target task. Unlike the case of
@@ -636,8 +633,6 @@ memory cgroup.
8.3 TODO
-- Implement madvise(2) to let users decide the vma to be moved or not to be
- moved.
- All of moving charge operations are done under cgroup_mutex. It's not good
behavior to hold the mutex too long, so we may need some trick.