Re: [PATCH] mm, THP, swap: fix allocating cluster for swapfile by mistake

On Thu, 20 Aug 2020 03:56:13 +0800 Gao Xiang hsiangkao@redhat.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 :(

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?