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Message-ID: <20130510140129.GA8008@cerebellum> Date: Fri, 10 May 2013 09:01:29 -0500 From: Seth Jennings <sjenning@...ux.vnet.ibm.com> To: Michal Hocko <mhocko@...e.cz> Cc: Dave Hansen <dave@...1.net>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, akpm@...ux-foundation.org, mgorman@...e.de, tim.c.chen@...ux.intel.com Subject: Re: [RFC][PATCH 1/7] defer clearing of page_private() for swap cache pages On Fri, May 10, 2013 at 11:26:49AM +0200, Michal Hocko wrote: > On Thu 09-05-13 17:07:39, Seth Jennings wrote: > > On Tue, May 07, 2013 at 02:19:55PM -0700, Dave Hansen wrote: > > > > > > From: Dave Hansen <dave.hansen@...ux.intel.com> > > > > > > There are only two callers of swapcache_free() which actually > > > pass in a non-NULL 'struct page'. Both of them > > > (__remove_mapping and delete_from_swap_cache()) create a > > > temporary on-stack 'swp_entry_t' and set entry.val to > > > page_private(). > > > > > > They need to do this since __delete_from_swap_cache() does > > > set_page_private(page, 0) and destroys the information. > > > > > > However, I'd like to batch a few of these operations on several > > > pages together in a new version of __remove_mapping(), and I > > > would prefer not to have to allocate temporary storage for > > > each page. The code is pretty ugly, and it's a bit silly > > > to create these on-stack 'swp_entry_t's when it is so easy to > > > just keep the information around in 'struct page'. > > > > > > There should not be any danger in doing this since we are > > > absolutely on the path of freeing these page. There is no > > > turning back, and no other rerferences can be obtained > > > after it comes out of the radix tree. > > > > I get a BUG on this one: > > > > [ 26.114818] ------------[ cut here ]------------ > > [ 26.115282] kernel BUG at mm/memcontrol.c:4111! > > [ 26.115282] invalid opcode: 0000 [#1] PREEMPT SMP > > [ 26.115282] Modules linked in: > > [ 26.115282] CPU: 3 PID: 5026 Comm: cc1 Not tainted 3.9.0+ #8 > > [ 26.115282] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007 > > [ 26.115282] task: ffff88007c1cdca0 ti: ffff88001b442000 task.ti: ffff88001b442000 > > [ 26.115282] RIP: 0010:[<ffffffff810ed425>] [<ffffffff810ed425>] __mem_cgroup_uncharge_common+0x255/0x2e0 > > [ 26.115282] RSP: 0000:ffff88001b443708 EFLAGS: 00010206 > > [ 26.115282] RAX: 4000000000090009 RBX: 0000000000000000 RCX: ffffc90000014001 > > [ 26.115282] RDX: 0000000000000000 RSI: 0000000000000002 RDI: ffffea00006e5b40 > > [ 26.115282] RBP: ffff88001b443738 R08: 0000000000000000 R09: 0000000000000000 > > [ 26.115282] R10: 0000000000000000 R11: 0000000000000000 R12: ffffea00006e5b40 > > [ 26.115282] R13: 0000000000000000 R14: ffffea00006e5b40 R15: 0000000000000002 > > [ 26.115282] FS: 00007fabd08ee700(0000) GS:ffff88007fd80000(0000) knlGS:0000000000000000 > > [ 26.115282] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 26.115282] CR2: 00007fabce27a000 CR3: 000000001985f000 CR4: 00000000000006a0 > > [ 26.115282] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > [ 26.115282] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > > [ 26.115282] Stack: > > [ 26.115282] ffffffff810dcbae ffff880064a0a500 0000000000000001 ffffea00006e5b40 > > [ 26.115282] ffffea00006e5b40 0000000000000001 ffff88001b443748 ffffffff810f0d05 > > [ 26.115282] ffff88001b443778 ffffffff810ddb3e ffff88001b443778 ffffea00006e5b40 > > [ 26.115282] Call Trace: > > [ 26.115282] [<ffffffff810dcbae>] ? swap_info_get+0x5e/0xe0 > > [ 26.115282] [<ffffffff810f0d05>] mem_cgroup_uncharge_swapcache+0x15/0x20 > > [ 26.115282] [<ffffffff810ddb3e>] swapcache_free+0x4e/0x70 > > [ 26.115282] [<ffffffff810b6e67>] __remove_mapping+0xd7/0x120 > > [ 26.115282] [<ffffffff810b8682>] shrink_page_list+0x5c2/0x920 > > [ 26.115282] [<ffffffff810b780e>] ? isolate_lru_pages.isra.37+0xae/0x120 > > [ 26.115282] [<ffffffff810b8ecf>] shrink_inactive_list+0x13f/0x380 > > [ 26.115282] [<ffffffff810b9350>] shrink_lruvec+0x240/0x4e0 > > [ 26.115282] [<ffffffff810b9656>] shrink_zone+0x66/0x1a0 > > [ 26.115282] [<ffffffff810ba1fb>] do_try_to_free_pages+0xeb/0x570 > > [ 26.115282] [<ffffffff810eb7d9>] ? lookup_page_cgroup_used+0x9/0x20 > > [ 26.115282] [<ffffffff810ba7af>] try_to_free_pages+0x9f/0xc0 > > [ 26.115282] [<ffffffff810b1357>] __alloc_pages_nodemask+0x5a7/0x970 > > [ 26.115282] [<ffffffff810cb2be>] handle_pte_fault+0x65e/0x880 > > [ 26.115282] [<ffffffff810cc7d9>] handle_mm_fault+0x139/0x1e0 > > [ 26.115282] [<ffffffff81027920>] __do_page_fault+0x160/0x460 > > [ 26.115282] [<ffffffff810d176c>] ? do_brk+0x1fc/0x360 > > [ 26.115282] [<ffffffff81212979>] ? lockdep_sys_exit_thunk+0x35/0x67 > > [ 26.115282] [<ffffffff81027c49>] do_page_fault+0x9/0x10 > > [ 26.115282] [<ffffffff813b4a72>] page_fault+0x22/0x30 > > [ 26.115282] Code: a9 00 00 08 00 0f 85 43 fe ff ff e9 b8 fe ff ff 66 0f 1f 44 00 00 41 8b 44 24 18 85 c0 0f 89 2b fe ff ff 0f 1f 00 e9 9d fe ff ff <0f> 0b 66 0f 1f 84 00 00 00 00 00 49 89 9c 24 48 0f 00 00 e9 0a > > [ 26.115282] RIP [<ffffffff810ed425>] __mem_cgroup_uncharge_common+0x255/0x2e0 > > [ 26.115282] RSP <ffff88001b443708> > > [ 26.171597] ---[ end trace 5e49a21e51452c24 ]--- > > > > > > mm/memcontrol:4111 > > VM_BUG_ON(PageSwapCache(page)); > > > > Seems that mem_cgroup_uncharge_swapcache, somewhat ironically expects the > > SwapCache flag to be unset already. > > > > Fix might be a simple as removing that VM_BUG_ON() but there might be more to > > it. There usually is :) > > This has been already fixed in the -mm tree > (http://git.kernel.org/cgit/linux/kernel/git/mhocko/mm.git/commit/?h=since-3.9&id=b341f7ffa5fe6ae11afa87e2fecc32c6093541f8) Ah yes, I even saw this patch come in now I see it again. I should have known! Seth -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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