Messages in this thread | | | Date | Tue, 12 May 2009 16:09:01 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 4/3] memcg: call uncharge_swapcache outside of tree_lock (Re: [PATCH 0/3] fix stale swap cache account leak in memcg v7) |
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On Tue, 12 May 2009 14:06:48 +0900 Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> On Tue, 12 May 2009 10:44:01 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > I hope this version gets acks.. > > == > > As Nishimura reported, there is a race at handling swap cache. > > > > Typical cases are following (from Nishimura's mail) > > > > > > == Type-1 == > > If some pages of processA has been swapped out, it calls free_swap_and_cache(). > > And if at the same time, processB is calling read_swap_cache_async() about > > a swap entry *that is used by processA*, a race like below can happen. > > > > processA | processB > > -------------------------------------+------------------------------------- > > (free_swap_and_cache()) | (read_swap_cache_async()) > > | swap_duplicate() > > | __set_page_locked() > > | add_to_swap_cache() > > swap_entry_free() == 0 | > > find_get_page() -> found | > > try_lock_page() -> fail & return | > > | lru_cache_add_anon() > > | doesn't link this page to memcg's > > | LRU, because of !PageCgroupUsed. > > > > This type of leak can be avoided by setting /proc/sys/vm/page-cluster to 0. > > > > > > == Type-2 == > > Assume processA is exiting and pte points to a page(!PageSwapCache). > > And processB is trying reclaim the page. > > > > processA | processB > > -------------------------------------+------------------------------------- > > (page_remove_rmap()) | (shrink_page_list()) > > mem_cgroup_uncharge_page() | > > ->uncharged because it's not | > > PageSwapCache yet. | > > So, both mem/memsw.usage | > > are decremented. | > > | add_to_swap() -> added to swap cache. > > > > If this page goes thorough without being freed for some reason, this page > > doesn't goes back to memcg's LRU because of !PageCgroupUsed. > > > > > > Considering Type-1, it's better to avoid swapin-readahead when memcg is used. > > swapin-readahead just read swp_entries which are near to requested entry. So, > > pages not to be used can be on memory (on global LRU). When memcg is used, > > this is not good behavior anyway. > > > > Considering Type-2, the page should be freed from SwapCache right after WriteBack. > > Free swapped out pages as soon as possible is a good nature to memcg, anyway. > > > > The patch set includes followng > > [1/3] add mem_cgroup_is_activated() function. which tell us memcg is _really_ used. > > [2/3] fix swap cache handling race by avoidng readahead. > > [3/3] fix swap cache handling race by check swapcount again. > > > > Result is good under my test. > > > These patches seem to work well on my side too. > > > BTW, we need one more fix which I found in a long term test last week. > After this patch, it survived all through the weekend in my test. > > I don't know why we've never hit this bug so far. > I think I hit it because my memcg_free_unused_swapcache() patch increases > the possibility of calling mem_cgroup_uncharge_swapcache(). > > Thanks, > Daisuke Nishimura. > === > From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > > memcg: call mem_cgroup_uncharge_swapcache() outside of tree_lock > > It's rare, but I hit a spinlock lockup. > > BUG: spinlock lockup on CPU#2, page01/24205, ffffffff806faf18 > Pid: 24205, comm: page01 Not tainted 2.6.30-rc4-5845621d #1 > Call Trace: > <IRQ> [<ffffffff80294f93>] ? test_clear_page_writeback+0x4d/0xff > [<ffffffff803752bc>] ? _raw_spin_lock+0xfb/0x122 > [<ffffffff804ee9ba>] ? _spin_lock_irqsave+0x59/0x70 > [<ffffffff80294f93>] ? test_clear_page_writeback+0x4d/0xff > [<ffffffff8029649c>] ? rotate_reclaimable_page+0x87/0x8e > [<ffffffff80294f93>] ? test_clear_page_writeback+0x4d/0xff > [<ffffffff8028d4ed>] ? end_page_writeback+0x1c/0x3d > [<ffffffff802ac4c6>] ? end_swap_bio_write+0x57/0x65 > [<ffffffff803516d9>] ? __end_that_request_first+0x1f3/0x2e4 > [<ffffffff803515f2>] ? __end_that_request_first+0x10c/0x2e4 > [<ffffffff803517e5>] ? end_that_request_data+0x1b/0x4c > [<ffffffff8035225a>] ? blk_end_io+0x1c/0x76 > [<ffffffffa0060702>] ? scsi_io_completion+0x1dc/0x467 [scsi_mod] > [<ffffffff80356394>] ? blk_done_softirq+0x66/0x76 > [<ffffffff8024002e>] ? __do_softirq+0xae/0x182 > [<ffffffff8020cb3c>] ? call_softirq+0x1c/0x2a > [<ffffffff8020de9a>] ? do_softirq+0x31/0x83 > [<ffffffff8020d57b>] ? do_IRQ+0xa9/0xbf > [<ffffffff8020c393>] ? ret_from_intr+0x0/0xf > <EOI> [<ffffffff8026fd56>] ? res_counter_uncharge+0x67/0x70 > [<ffffffff802bf04a>] ? __mem_cgroup_uncharge_common+0xbd/0x158 > [<ffffffff802a0f55>] ? unmap_vmas+0x7ef/0x829 > [<ffffffff802a8a3a>] ? page_remove_rmap+0x1b/0x36 > [<ffffffff802a0c11>] ? unmap_vmas+0x4ab/0x829 > [<ffffffff802a5243>] ? exit_mmap+0xa7/0x11c > [<ffffffff80239009>] ? mmput+0x41/0x9f > [<ffffffff8023cf7b>] ? exit_mm+0x101/0x10c > [<ffffffff8023e481>] ? do_exit+0x1a4/0x61e > [<ffffffff80259391>] ? trace_hardirqs_on_caller+0x11d/0x148 > [<ffffffff8023e96e>] ? do_group_exit+0x73/0xa5 > [<ffffffff8023e9b2>] ? sys_exit_group+0x12/0x16 > [<ffffffff8020b96b>] ? system_call_fastpath+0x16/0x1b > > This is caused when: > > CPU1: __mem_cgroup_uncharge_common(), which is holding page_cgroup lock, > is interuppted and end_swap_bio_write(), which tries to hold > swapper_space.tree_lock, is called in the interrupt context. > CPU2: mem_cgroup_uncharge_swapcache(), which is called under swapper_space.tree_lock, > is spinning at lock_page_cgroup() in __mem_cgroup_uncharge_common(). > > IIUC, there is no need that mem_cgroup_uncharge_swapcache() should be called under > swapper_space.tree.lock, so move it outside the tree_lock. >
I understand the problem, but, wait a bit. NACK to this patch itself.
1. I placed _uncharge_ inside tree_lock because __remove_from_page_cache() does. (i.e. using the same logic.) So, plz change both logic at once.(change caller of mem_cgroup_uncharge_cache_page())
2. Shouldn't we disable IRQ while __mem_cgroup_uncharge_common() rather than moving function ?
Thanks, -Kame
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > --- > include/linux/swap.h | 5 +++++ > mm/memcontrol.c | 2 +- > mm/swap_state.c | 4 +--- > mm/vmscan.c | 1 + > 4 files changed, 8 insertions(+), 4 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index caf0767..6ea541d 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -431,6 +431,11 @@ static inline swp_entry_t get_swap_page(void) > #define has_swap_token(x) 0 > #define disable_swap_token() do { } while(0) > > +static inline void > +mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) > +{ > +} > + > #endif /* CONFIG_SWAP */ > #endif /* __KERNEL__*/ > #endif /* _LINUX_SWAP_H */ > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 0c9c1ad..379f200 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1489,7 +1489,7 @@ void mem_cgroup_uncharge_cache_page(struct page *page) > } > > /* > - * called from __delete_from_swap_cache() and drop "page" account. > + * called after __delete_from_swap_cache() and drop "page" account. > * memcg information is recorded to swap_cgroup of "ent" > */ > void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) > diff --git a/mm/swap_state.c b/mm/swap_state.c > index e389ef2..7624c89 100644 > --- a/mm/swap_state.c > +++ b/mm/swap_state.c > @@ -109,8 +109,6 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask) > */ > void __delete_from_swap_cache(struct page *page) > { > - swp_entry_t ent = {.val = page_private(page)}; > - > VM_BUG_ON(!PageLocked(page)); > VM_BUG_ON(!PageSwapCache(page)); > VM_BUG_ON(PageWriteback(page)); > @@ -121,7 +119,6 @@ void __delete_from_swap_cache(struct page *page) > total_swapcache_pages--; > __dec_zone_page_state(page, NR_FILE_PAGES); > INC_CACHE_INFO(del_total); > - mem_cgroup_uncharge_swapcache(page, ent); > } > > /** > @@ -191,6 +188,7 @@ void delete_from_swap_cache(struct page *page) > __delete_from_swap_cache(page); > spin_unlock_irq(&swapper_space.tree_lock); > > + mem_cgroup_uncharge_swapcache(page, entry); > swap_free(entry); > page_cache_release(page); > } > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 337be66..e674cd1 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -470,6 +470,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page) > swp_entry_t swap = { .val = page_private(page) }; > __delete_from_swap_cache(page); > spin_unlock_irq(&mapping->tree_lock); > + mem_cgroup_uncharge_swapcache(page, swap); > swap_free(swap); > } else { > __remove_from_page_cache(page); >
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