From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4C9ADC433E0 for ; Wed, 3 Jun 2020 23:01:40 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0BE982100A for ; Wed, 3 Jun 2020 23:01:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="GHVvbXDe" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0BE982100A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7561428005E; Wed, 3 Jun 2020 19:01:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7017E280003; Wed, 3 Jun 2020 19:01:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6413928005E; Wed, 3 Jun 2020 19:01:37 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0223.hostedemail.com [216.40.44.223]) by kanga.kvack.org (Postfix) with ESMTP id 4A457280003 for ; Wed, 3 Jun 2020 19:01:37 -0400 (EDT) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 0C3B6180AD806 for ; Wed, 3 Jun 2020 23:01:37 +0000 (UTC) X-FDA: 76889424234.26.nerve05_2b22fd84e1811 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin26.hostedemail.com (Postfix) with ESMTP id D2AA81804B654 for ; Wed, 3 Jun 2020 23:01:36 +0000 (UTC) X-HE-Tag: nerve05_2b22fd84e1811 X-Filterd-Recvd-Size: 4540 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf45.hostedemail.com (Postfix) with ESMTP for ; Wed, 3 Jun 2020 23:01:36 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0A5EF20B80; Wed, 3 Jun 2020 23:01:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591225295; bh=b7DuBXlMRxHGJ5UaiVjEkhyRTs7uLpBdMvbfxbp0YrA=; h=Date:From:To:Subject:In-Reply-To:From; b=GHVvbXDeJnwzZOuev3gXlHBAaW8cLjGhreaZ+TJs7BROixgBIi1c6eZnqps/VY24U LV8nCbEmcwcjmJtoYDEMMfGQm6ybefECWfAwCPh88vfpu5JrF6VouTvw+ttlz3Jfrz 88MdIhpIfxD2VtzwbqF4+JcMU2bJl3NWSINb910o= Date: Wed, 03 Jun 2020 16:01:34 -0700 From: Andrew Morton To: akpm@linux-foundation.org, alex.shi@linux.alibaba.com, bsingharora@gmail.com, guro@fb.com, hannes@cmpxchg.org, hughd@google.com, iamjoonsoo.kim@lge.com, kirill@shutemov.name, linux-mm@kvack.org, mhocko@suse.com, mm-commits@vger.kernel.org, shakeelb@google.com, torvalds@linux-foundation.org Subject: [patch 086/131] mm: shmem: remove rare optimization when swapin races with hole punching Message-ID: <20200603230134.IaJjlfqVp%akpm@linux-foundation.org> In-Reply-To: <20200603155549.e041363450869eaae4c7f05b@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Rspamd-Queue-Id: D2AA81804B654 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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: From: Johannes Weiner Subject: mm: shmem: remove rare optimization when swapin races with hole punching Commit 215c02bc33bb ("tmpfs: fix shmem_getpage_gfp() VM_BUG_ON") recognized that hole punching can race with swapin and removed the BUG_ON() for a truncated entry from the swapin path. The patch also added a swapcache deletion to optimize this rare case: Since swapin has the page locked, and free_swap_and_cache() merely trylocks, this situation can leave the page stranded in swapcache. Usually, page reclaim picks up stale swapcache pages, and the race can happen at any other time when the page is locked. (The same happens for non-shmem swapin racing with page table zapping.) The thinking here was: we already observed the race and we have the page locked, we may as well do the cleanup instead of waiting for reclaim. However, this optimization complicates the next patch which moves the cgroup charging code around. As this is just a minor speedup for a race condition that is so rare that it required a fuzzer to trigger the original BUG_ON(), it's no longer worth the complications. Link: http://lkml.kernel.org/r/20200511181056.GA339505@cmpxchg.org Signed-off-by: Johannes Weiner Suggested-by: Hugh Dickins Acked-by: Hugh Dickins Cc: Alex Shi Cc: Joonsoo Kim Cc: Shakeel Butt Cc: "Kirill A. Shutemov" Cc: Michal Hocko Cc: Roman Gushchin Cc: Balbir Singh Signed-off-by: Andrew Morton --- mm/shmem.c | 25 +++++++------------------ 1 file changed, 7 insertions(+), 18 deletions(-) --- a/mm/shmem.c~mm-shmem-remove-rare-optimization-when-swapin-races-with-hole-punching +++ a/mm/shmem.c @@ -1665,27 +1665,16 @@ static int shmem_swapin_page(struct inod } error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg); - if (!error) { - error = shmem_add_to_page_cache(page, mapping, index, - swp_to_radix_entry(swap), gfp); - /* - * We already confirmed swap under page lock, and make - * no memory allocation here, so usually no possibility - * of error; but free_swap_and_cache() only trylocks a - * page, so it is just possible that the entry has been - * truncated or holepunched since swap was confirmed. - * shmem_undo_range() will have done some of the - * unaccounting, now delete_from_swap_cache() will do - * the rest. - */ - if (error) { - mem_cgroup_cancel_charge(page, memcg); - delete_from_swap_cache(page); - } - } if (error) goto failed; + error = shmem_add_to_page_cache(page, mapping, index, + swp_to_radix_entry(swap), gfp); + if (error) { + mem_cgroup_cancel_charge(page, memcg); + goto failed; + } + mem_cgroup_commit_charge(page, memcg, true); spin_lock_irq(&info->lock); _