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Fri, 16 Sep 2022 08:40:59 +0000 Date: Fri, 16 Sep 2022 09:40:59 +0100 From: Matthew Wilcox To: Hongchen Zhang Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/vmscan: don't scan adjust too much if current is not kswapd Message-ID: References: <20220914023318.549118-1-zhanghongchen@loongson.cn> <20220914155142.bf388515a39fb45bae987231@linux-foundation.org> <6bcb4883-03d0-88eb-4c42-84fff0a9a141@loongson.cn> <54813a74-cc0e-e470-c632-78437a0d0ad4@loongson.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=FfvFaEfa; spf=none (imf16.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663317662; a=rsa-sha256; cv=none; b=6PFxbjKTWokCyXY7byMdisV0xqcKvlgkkFHywTNuGIuj5FkgsPZa193sLk7rZuILvO9jGJ uliDwyh4OxMLKWQISMHXc9X72jJSmddO5wmnxc/qFPGskkVJi5uyGwbsNVBd4WxRMSz1S8 qYlNMoxYXHSl9rG1U4NaaITK5JaP9mY= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663317662; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=qfHTiySpHhHOQIjP3+B153jEM36eOAvO8iYY29vr6qc=; b=XvNMuNdUbaza8f2NE/oaYdLb8efcCsvY/9LRij1dgf49h/Y9o8MceRvlw3VP92ud4PG/bG ffqSUn1uhlxYyrwPMmaN0erd9aTw30hdeEPxH0gCA6fEJP6Dc2Jt+fYBspbjQQUhiQXqqa qoKQorHLQGL93LC0lxp5w6XxfGRecnw= X-Rspamd-Queue-Id: 1EA4618009B X-Rspam-User: Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=FfvFaEfa; spf=none (imf16.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-Stat-Signature: aftrc5qncjhtdw34q4ywkzgozjzmrse4 X-Rspamd-Server: rspam04 X-HE-Tag: 1663317661-966018 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Sep 16, 2022 at 08:57:50AM +0800, Hongchen Zhang wrote: > Hi Andrew , > > On 2022/9/15 pm 5:00, Matthew Wilcox wrote: > > On Thu, Sep 15, 2022 at 04:02:41PM +0800, Hongchen Zhang wrote: > > > Hi Matthew, > > > On 2022/9/15 pm 3:28, Matthew Wilcox wrote: > > > > On Thu, Sep 15, 2022 at 09:19:48AM +0800, Hongchen Zhang wrote: > > > > > [ 3748.453561] INFO: task float_bessel:77920 blocked for more than 120 > > > > > seconds. > > > > > [ 3748.460839] Not tainted 5.15.0-46-generic #49-Ubuntu > > > > > [ 3748.466490] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables > > > > > this message. > > > > > [ 3748.474618] task:float_bessel state:D stack: 0 pid:77920 ppid: > > > > > 77327 flags:0x00004002 > > > > > [ 3748.483358] Call Trace: > > > > > [ 3748.485964] > > > > > [ 3748.488150] __schedule+0x23d/0x590 > > > > > [ 3748.491804] schedule+0x4e/0xc0 > > > > > [ 3748.495038] rwsem_down_read_slowpath+0x336/0x390 > > > > > [ 3748.499886] ? copy_user_enhanced_fast_string+0xe/0x40 > > > > > [ 3748.505181] down_read+0x43/0xa0 > > > > > [ 3748.508518] do_user_addr_fault+0x41c/0x670 > > > > > [ 3748.512799] exc_page_fault+0x77/0x170 > > > > > [ 3748.516673] asm_exc_page_fault+0x26/0x30 > > > > > [ 3748.520824] RIP: 0010:copy_user_enhanced_fast_string+0xe/0x40 > > > > > [ 3748.526764] Code: 89 d1 c1 e9 03 83 e2 07 f3 48 a5 89 d1 f3 a4 31 c0 0f > > > > > 01 ca c3 cc cc cc cc 0f 1f 00 0f 01 cb 83 fa 40 0f 82 70 ff ff ff 89 d1 > > > > > a4 31 c0 0f 01 ca c3 cc cc cc cc 66 08 > > > > > [ 3748.546120] RSP: 0018:ffffaa9248fffb90 EFLAGS: 00050206 > > > > > [ 3748.551495] RAX: 00007f99faa1a010 RBX: ffffaa9248fffd88 RCX: > > > > > 0000000000000010 > > > > > [ 3748.558828] RDX: 0000000000001000 RSI: ffff9db397ab8ff0 RDI: > > > > > 00007f99faa1a000 > > > > > [ 3748.566160] RBP: ffffaa9248fffbf0 R08: ffffcc2fc2965d80 R09: > > > > > 0000000000000014 > > > > > [ 3748.573492] R10: 0000000000000000 R11: 0000000000000014 R12: > > > > > 0000000000001000 > > > > > [ 3748.580858] R13: 0000000000001000 R14: 0000000000000000 R15: > > > > > ffffaa9248fffd98 > > > > > [ 3748.588196] ? copy_page_to_iter+0x10e/0x400 > > > > > [ 3748.592614] filemap_read+0x174/0x3e0 > > > > > > > > Interesting; it wasn't the process itself which triggered the page > > > > fault; the process called read() and the kernel took the page fault to > > > > satisfy the read() call. > > > > > > > > > [ 3748.596354] ? ima_file_check+0x6a/0xa0 > > > > > [ 3748.600301] generic_file_read_iter+0xe5/0x150 > > > > > [ 3748.604884] ext4_file_read_iter+0x5b/0x190 > > > > > [ 3748.609164] ? aa_file_perm+0x102/0x250 > > > > > [ 3748.613125] new_sync_read+0x10d/0x1a0 > > > > > [ 3748.617009] vfs_read+0x103/0x1a0 > > > > > [ 3748.620423] ksys_read+0x67/0xf0 > > > > > [ 3748.623743] __x64_sys_read+0x19/0x20 > > > > > [ 3748.627511] do_syscall_64+0x59/0xc0 > > > > > [ 3748.631203] ? syscall_exit_to_user_mode+0x27/0x50 > > > > > [ 3748.636144] ? do_syscall_64+0x69/0xc0 > > > > > [ 3748.639992] ? exit_to_user_mode_prepare+0x96/0xb0 > > > > > [ 3748.644931] ? irqentry_exit_to_user_mode+0x9/0x20 > > > > > [ 3748.649872] ? irqentry_exit+0x1d/0x30 > > > > > [ 3748.653737] ? exc_page_fault+0x89/0x170 > > > > > [ 3748.657795] entry_SYSCALL_64_after_hwframe+0x61/0xcb > > > > > [ 3748.663030] RIP: 0033:0x7f9a852989cc > > > > > [ 3748.666713] RSP: 002b:00007f9a8497dc90 EFLAGS: 00000246 ORIG_RAX: > > > > > 0000000000000000 > > > > > [ 3748.674487] RAX: ffffffffffffffda RBX: 00007f9a8497f5c0 RCX: > > > > > 00007f9a852989cc > > > > > [ 3748.681817] RDX: 0000000000027100 RSI: 00007f99faa18010 RDI: > > > > > 0000000000000061 > > > > > [ 3748.689150] RBP: 00007f9a8497dd60 R08: 0000000000000000 R09: > > > > > 00007f99faa18010 > > > > > [ 3748.696493] R10: 0000000000000000 R11: 0000000000000246 R12: > > > > > 00007f99faa18010 > > > > > [ 3748.703841] R13: 00005605e11c406f R14: 0000000000000001 R15: > > > > > 0000000000027100 > > > > > > > > ORIG_RAX is 0, which matches sys_read. > > > > RDI is file descriptor 0x61 > > > > RSI is plausibly a userspace pointer, 0x7f99faa18010 > > > > RDX is the length, 0x27100 or 160kB. > > > > > > > > That all seems reasonable. > > > > > > > > What I really want to know is who is _holding_ the lock. We stash > > > > a pointer to the task_struct in 'owner', so we could clearly find this > > > > out in the 'blocked for too long' report, and print their stack trace. > > > > > > > As described in the comment for __rwsem_set_reader_owned,it is hard to track > > > read owners.So we could not clearly find out who blocked the process,it was > > > caused by multiple tasks. > > > > Readers don't block readers. You have a reader here, so it's being > > blocked by a writer. And that writer's task_struct is stashed in > > rwsem->owner. It would be nice if we dumped that information > > automatically ... but we don't do that today. Perhaps you could > > grab that information from a crash dump if you have one. > > > > > > You must have done something like this already in order to deduce that > > > > it was the direct reclaim path that was the problem? > > > > > > > The method we used is to track the direct reclaim using the > > > trace_mm_vmscan_direct_reclaim_{begin,end} interface.When the problem > > > occurred,we could get a very large "nr_reclaimed" which is not a desirable > > > value for process except kswapd. > > > > I disagree. If a process needs to allocate memory then it should be > > paying the cost of reclaiming that memory itself. kswapd is a last > > resort to reclaim memory when we have a workload (eg a network router) > > that does its memory allocation primarily in interrupt context. > > > What's your opinion about this scan adjust issue? Is there a better way to > fix this issue? Yes, but we need you to gather more information about what's causing the issue before we can suggest what that is.