On Sat, Jun 16, 2012 at 2:34 PM, Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > (2012/06/16 0:32), Greg Thelen wrote: >> >> On Fri, Jun 15 2012, Sha Zhengju wrote: >> >>> This patch adds memcg routines to count dirty pages. I notice that >>> the list has talked about per-cgroup dirty page limiting >>> (http://lwn.net/Articles/455341/) before, but it did not get merged. >> >> >> Good timing, I was just about to make another effort to get some of >> these patches upstream. Like you, I was going to start with some basic >> counters. >> >> Your approach is similar to what I have in mind. While it is good to >> use the existing PageDirty flag, rather than introducing a new >> page_cgroup flag, there are locking complications (see below) to handle >> races between moving pages between memcg and the pages being {un}marked >> dirty. >> >>> I've no idea how is this going now, but maybe we can add per cgroup >>> dirty pages accounting first. This allows the memory controller to >>> maintain an accurate view of the amount of its memory that is dirty >>> and can provide some infomation while group's direct reclaim is working. >>> >>> After commit 89c06bd5 (memcg: use new logic for page stat accounting), >>> we do not need per page_cgroup flag anymore and can directly use >>> struct page flag. >>> >>> >>> Signed-off-by: Sha Zhengju<handai.szj@xxxxxxxxxx> >>> --- >>> include/linux/memcontrol.h | 1 + >>> mm/filemap.c | 1 + >>> mm/memcontrol.c | 32 +++++++++++++++++++++++++------- >>> mm/page-writeback.c | 2 ++ >>> mm/truncate.c | 1 + >>> 5 files changed, 30 insertions(+), 7 deletions(-) >>> >>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >>> index a337c2e..8154ade 100644 >>> --- a/include/linux/memcontrol.h >>> +++ b/include/linux/memcontrol.h >>> @@ -39,6 +39,7 @@ enum mem_cgroup_stat_index { >>> MEM_CGROUP_STAT_FILE_MAPPED, /* # of pages charged as file rss */ >>> MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */ >>> MEM_CGROUP_STAT_DATA, /* end of data requires synchronization */ >>> + MEM_CGROUP_STAT_FILE_DIRTY, /* # of dirty pages in page cache */ >>> MEM_CGROUP_STAT_NSTATS, >>> }; >>> >>> diff --git a/mm/filemap.c b/mm/filemap.c >>> index 79c4b2b..5b5c121 100644 >>> --- a/mm/filemap.c >>> +++ b/mm/filemap.c >>> @@ -141,6 +141,7 @@ void __delete_from_page_cache(struct page *page) >>> * having removed the page entirely. >>> */ >>> if (PageDirty(page)&& mapping_cap_account_dirty(mapping)) { >>> + mem_cgroup_dec_page_stat(page, >>> MEM_CGROUP_STAT_FILE_DIRTY); >> >> >> You need to use mem_cgroup_{begin,end}_update_page_stat around critical >> sections that: >> 1) check PageDirty >> 2) update MEM_CGROUP_STAT_FILE_DIRTY counter >> >> This protects against the page from being moved between memcg while >> accounting. Same comment applies to all of your new calls to >> mem_cgroup_{dec,inc}_page_stat. For usage pattern, see >> page_add_file_rmap. >> > > If you feel some difficulty with mem_cgroup_{begin,end}_update_page_stat(), > please let me know...I hope they should work enough.... > Hi, Kame While digging into the bigger lock of mem_cgroup_{begin,end}_update_page_stat(), I find the reality is more complex than I thought. Simply stated, modifying page info and update page stat may be wide apart and in different level (eg. mm&fs), so if we use the big lock it may lead to scalability and maintainability issues. For example: mem_cgroup_begin_update_page_stat() modify page information => TestSetPageDirty in ceph_set_page_dirty() (fs/ceph/addr.c) XXXXXX => other fs operations mem_cgroup_update_page_stat() => account_page_dirtied() in mm/page-writeback.c mem_cgroup_end_update_page_stat(). We can choose to get lock in higher level meaning vfs set_page_dirty() but this may span too much and can also have some missing cases. What's your opinion of this problem? Thanks, Sha -- 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/ . Don't email: <a href