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Date: Wed, 19 Aug 2020 16:44:05 -0400 From: Rafael Aquini <aquini@...hat.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Gao Xiang <hsiangkao@...hat.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Carlos Maiolino <cmaiolino@...hat.com>, Eric Sandeen <esandeen@...hat.com>, "Huang, Ying" <ying.huang@...el.com>, stable <stable@...r.kernel.org> Subject: Re: [PATCH] mm, THP, swap: fix allocating cluster for swapfile by mistake On Wed, Aug 19, 2020 at 01:05:06PM -0700, Andrew Morton wrote: > On Thu, 20 Aug 2020 03:56:13 +0800 Gao Xiang <hsiangkao@...hat.com> wrote: > > > SWP_FS doesn't mean the device is file-backed swap device, > > which just means each writeback request should go through fs > > by DIO. Or it'll just use extents added by .swap_activate(), > > but it also works as file-backed swap device. > > This is very hard to understand :( > I'll work with Gao to rephrase that message. Sorry! > > So in order to achieve the goal of the original patch, > > SWP_BLKDEV should be used instead. > > > > FS corruption can be observed with SSD device + XFS + > > fragmented swapfile due to CONFIG_THP_SWAP=y. > > > > Fixes: f0eea189e8e9 ("mm, THP, swap: Don't allocate huge cluster for file backed swap device") > > Fixes: 38d8b4e6bdc8 ("mm, THP, swap: delay splitting THP during swap out") > > Why do you think it has taken three years to discover this? > My bet here is that it's rare to go for a swapfile on non-rotational devices, and even rarer to create the swapfile when the filesystem is already fragmented. RHEL-8, v4.18-based, is starting to see more adpters among Red Hat's customer base, thus the report now. We are also working on a secondary issue related to CONFIG_THP_SWAP, as well, where the deferred THP split registered shriker goes for a NULL pointer dereference in case the swap device is backed by a rotational drive. -- Rafael
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