WSL2-Linux-Kernel/Documentation/controllers
KAMEZAWA Hiroyuki 03f3c43364 memcg: fix swap accounting leak
Fix swapin charge operation of memcg.

Now, memcg has hooks to swap-out operation and checks SwapCache is really
unused or not.  That check depends on contents of struct page.  I.e.  If
PageAnon(page) && page_mapped(page), the page is recoginized as
still-in-use.

Now, reuse_swap_page() calles delete_from_swap_cache() before establishment
of any rmap. Then, in followinig sequence

	(Page fault with WRITE)
	try_charge() (charge += PAGESIZE)
	commit_charge() (Check page_cgroup is used or not..)
	reuse_swap_page()
		-> delete_from_swapcache()
			-> mem_cgroup_uncharge_swapcache() (charge -= PAGESIZE)
	......
New charge is uncharged soon....
To avoid this,  move commit_charge() after page_mapcount() goes up to 1.
By this,

	try_charge()		(usage += PAGESIZE)
	reuse_swap_page()	(may usage -= PAGESIZE if PCG_USED is set)
	commit_charge()		(If page_cgroup is not marked as PCG_USED,
				 add new charge.)
Accounting will be correct.

Changelog (v2) -> (v3)
  - fixed invalid charge to swp_entry==0.
  - updated documentation.
Changelog (v1) -> (v2)
  - fixed comment.

[nishimura@mxp.nes.nec.co.jp: swap accounting leak doc fix]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Tested-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-01-08 08:31:10 -08:00
..
cpuacct.txt sched: add hierarchical accounting to cpu accounting controller 2008-11-11 12:13:28 +01:00
devices.txt devcgroup: fix odd behaviour when writing 'a' to devices.allow 2008-07-04 10:40:10 -07:00
memcg_test.txt memcg: fix swap accounting leak 2009-01-08 08:31:10 -08:00
memory.txt memcg: swappiness 2009-01-08 08:31:08 -08:00
resource_counter.txt memcgroups: add a document describing the resource counter abstraction 2008-04-29 08:06:10 -07:00