Hi Miklos, On Wed, Jul 23, 2014 at 08:08:57PM +0200, Miklos Szeredi wrote: > On Wed, Jul 23, 2014 at 5:06 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > Can the new page be anything else than previous page cache? > > It could be an ordinary pipe buffer too. Stealable as well (see > generic_pipe_buf_steal()). Okay, they need charging, so we can't get rid of mem_cgroup_migrate() in replace_page_cache(). With the fuse example mount you described I can trigger the current code to blow up, so below is a fix to check if the target page is already charged. On an unrelated note, while playing around with the fuse example mount and heavy swapping workloads I get the following in dmesg (changed fuse_check_page() to use dump_page(), will send a patch later): [ 298.771921] page:ffffea000468cb80 count:1 mapcount:0 mapping: (null) index:0x1e852f8 [ 298.780517] page flags: 0x5fffc000080029(locked|uptodate|lru|swapbacked) [ 298.787385] page dumped because: fuse: trying to steal weird page [ 298.793500] pc:ffff880215f232e0 pc->flags:7 pc->mem_cgroup:ffff880216c23000 [ 298.801031] page:ffffea0004662f00 count:1 mapcount:0 mapping: (null) index:0x1e85324 [ 298.809689] page flags: 0x5fffc000080029(locked|uptodate|lru|swapbacked) [ 298.816615] page dumped because: fuse: trying to steal weird page [ 298.822791] pc:ffff880215f18bc0 pc->flags:7 pc->mem_cgroup:ffff880216c23000 etc. Somehow the page stealing ends up taking out anonymous pages, but it must be a race condition as it happens rarely and irregularly. --- >From 2c3525cb556313936845a7c57f4c4adc655b6680 Mon Sep 17 00:00:00 2001 From: Johannes Weiner <hannes@xxxxxxxxxxx> Date: Wed, 23 Jul 2014 15:00:15 -0400 Subject: [patch] mm: memcontrol: rewrite uncharge API fix - page cache migration 2 In case of fuse page cache replacement the target page in migration can already be charged when splice steals it from page cache. That triggers the !PageCgrouUsed() assertion during commit: [ 755.141095] page:ffffea00031f9b00 count:2 mapcount:0 mapping:ffff8800c84d1858 index:0x0 [ 755.141097] page flags: 0x3fffc000000029(locked|uptodate|lru) [ 755.141098] page dumped because: VM_BUG_ON_PAGE(PageCgroupUsed(pc)) [ 755.141098] pc:ffff880215cfe6c0 pc->flags:7 pc->mem_cgroup:ffff880216c23000 [ 755.141113] ------------[ cut here ]------------ [ 755.141113] kernel BUG at /home/hannes/src/linux/linux/mm/memcontrol.c:2736! [ 755.141115] invalid opcode: 0000 [#1] SMP [ 755.141117] CPU: 0 PID: 342 Comm: lt-fusexmp_fh Not tainted 3.16.0-rc5-mm1-00502-g5e5b90c20054 #367 [ 755.141117] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./H61M-DGS, BIOS P1.30 05/10/2012 [ 755.141118] task: ffff880213104580 ti: ffff8800c9204000 task.ti: ffff8800c9204000 [ 755.141121] RIP: 0010:[<ffffffff81188497>] [<ffffffff81188497>] commit_charge+0xa7/0xb0 [ 755.141122] RSP: 0018:ffff8800c9207c18 EFLAGS: 00010286 [ 755.141123] RAX: 000000000000003f RBX: ffffea00031f9b00 RCX: 0000000000004c4b [ 755.141123] RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffff880213104580 [ 755.141124] RBP: ffff8800c9207c40 R08: 0000000000000001 R09: 0000000000000000 [ 755.141124] R10: 0000000000000000 R11: 0000000000000000 R12: ffff880216c23000 [ 755.141125] R13: 0000000000000001 R14: ffff8800c84d1858 R15: 0000000000000000 [ 755.141125] FS: 00007fc15f7fe700(0000) GS:ffff88021f200000(0000) knlGS:0000000000000000 [ 755.141126] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 755.141127] CR2: 00007f693db3b6b0 CR3: 0000000211d54000 CR4: 00000000000407f0 [ 755.141127] Stack: [ 755.141128] ffffea00031f8480 ffffea00031f9b00 ffffea00031f8480 ffffea00031f9b00 [ 755.141129] 0000000000000000 ffff8800c9207c78 ffffffff8118e283 00000001c9207c60 [ 755.141130] ffff880215cfe120 00000001c9207c78 ffffea00031f9b00 ffffea00031f8480 [ 755.141131] Call Trace: [ 755.141133] [<ffffffff8118e283>] mem_cgroup_migrate+0xe3/0x210 [ 755.141135] [<ffffffff8111a086>] replace_page_cache_page+0xf6/0x1c0 [ 755.141137] [<ffffffff8127aceb>] fuse_copy_page+0x1bb/0x5f0 [ 755.141138] [<ffffffff8127b20f>] fuse_copy_args+0xef/0x140 [ 755.141140] [<ffffffff8127caba>] fuse_dev_do_write+0x7ba/0xd30 [ 755.141143] [<ffffffff8109518d>] ? trace_hardirqs_on_caller+0x15d/0x200 [ 755.141146] [<ffffffff816a83ea>] ? __mutex_unlock_slowpath+0xaa/0x180 [ 755.141147] [<ffffffff8109518d>] ? trace_hardirqs_on_caller+0x15d/0x200 [ 755.141148] [<ffffffff8109523d>] ? trace_hardirqs_on+0xd/0x10 [ 755.141150] [<ffffffff8127d2b2>] fuse_dev_splice_write+0x282/0x360 [ 755.141152] [<ffffffff811c4ce1>] SyS_splice+0x351/0x800 [ 755.141153] [<ffffffff8109518d>] ? trace_hardirqs_on_caller+0x15d/0x200 [ 755.141155] [<ffffffff816ab192>] system_call_fastpath+0x16/0x1b [ 755.141166] Code: 07 48 89 10 8b 75 e4 e8 f8 fd ff ff 48 83 c4 10 5b 41 5c 41 5d 5d c3 0f 1f 44 00 00 48 c7 c6 68 0b 9c 81 48 89 df e8 e9 a2 f9 ff <0f> 0b 0f 1f 80 00 00 00 00 66 66 66 66 90 48 39 f7 74 26 48 85 [ 755.141167] RIP [<ffffffff81188497>] commit_charge+0xa7/0xb0 [ 755.141167] RSP <ffff8800c9207c18> [ 755.141665] ---[ end trace 2d0ea36c8e3ded5b ]--- If the target page is already charged, just leave it as is and abort the charge migration attempt. Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> --- mm/memcontrol.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b7c9a202dee9..3eaa6e83c168 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6660,6 +6660,12 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage, if (mem_cgroup_disabled()) return; + /* Page cache replacement: new page already charged? */ + pc = lookup_page_cgroup(newpage); + if (PageCgroupUsed(pc)) + return; + + /* Re-entrant migration: old page already uncharged? */ pc = lookup_page_cgroup(oldpage); if (!PageCgroupUsed(pc)) return; -- 2.0.0 -- 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=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>