From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [merged] =?US-ASCII?Q?mm-shmem-remove-rare-optimization-when-swapin-races-with-hol?= =?US-ASCII?Q?e-punching.patch?= removed from -mm tree Date: Thu, 04 Jun 2020 10:19:56 -0700 Message-ID: <20200604171956.Bdfs6MSnu%akpm@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: Received: from mail.kernel.org ([198.145.29.99]:41890 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730043AbgFDRT6 (ORCPT ); Thu, 4 Jun 2020 13:19:58 -0400 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: alex.shi@linux.alibaba.com, bsingharora@gmail.com, guro@fb.com, hannes@cmpxchg.org, hughd@google.com, iamjoonsoo.kim@lge.com, kirill@shutemov.name, mhocko@suse.com, mm-commits@vger.kernel.org, shakeelb@google.com The patch titled Subject: mm: shmem: remove rare optimization when swapin races with hole punching has been removed from the -mm tree. Its filename was mm-shmem-remove-rare-optimization-when-swapin-races-with-hole-punching.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ 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); _ Patches currently in -mm which might be from hannes@cmpxchg.org are