On Fri, 9 Dec 2011 12:37:01 -0800 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, 8 Dec 2011 16:18:29 +0900 > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > > commit ef6a3c6311 adds a function replace_page_cache_page(). This > > function replaces a page in radix-tree with a new page. > > At doing this, memory cgroup need to fix up the accounting information. > > memcg need to check PCG_USED bit etc. > > > > In some(many?) case, 'newpage' is on LRU before calling replace_page_cache(). > > So, memcg's LRU accounting information should be fixed, too. > > > > This patch adds mem_cgroup_replace_page_cache() and removing old hooks. > > In that function, old pages will be unaccounted without touching res_counter > > and new page will be accounted to the memcg (of old page). At overwriting > > pc->mem_cgroup of newpage, take zone->lru_lock and avoid race with > > LRU handling. > > > > Background: > > replace_page_cache_page() is called by FUSE code in its splice() handling. > > Here, 'newpage' is replacing oldpage but this newpage is not a newly allocated > > page and may be on LRU. LRU mis-accounting will be critical for memory cgroup > > because rmdir() checks the whole LRU is empty and there is no account leak. > > If a page is on the other LRU than it should be, rmdir() will fail. > > > > Changelog: v1 -> v2 > > - fixed mem_cgroup_disabled() check missing. > > - added comments. > > > > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > --- > > include/linux/memcontrol.h | 6 ++++++ > > mm/filemap.c | 18 ++---------------- > > mm/memcontrol.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 52 insertions(+), 16 deletions(-) > > It's a relatively intrusive patch and I'm a bit concerned about > feeding it into 3.2. > > How serious is the bug, and which kernel version(s) do you think we > should fix it in? This bug was added by commit ef6a3c63112e (2011 Mar), but no bug report yet. I guess there are not many people who use memcg and FUSE at the same time with upstream kernels. The result of this bug is that admin cannot destroy a memcg because of account leak. So, no panic, no deadlock. And, even if an active cgroup exist, umount can succseed. So no problem at shutdown. I want this fix should be merged when/after unify-lru works goes to upstream. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>