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Date: Thu, 26 Nov 2020 20:42:11 +0100 From: Vlastimil Babka <vbabka@...e.cz> To: Rik van Riel <riel@...riel.com>, hughd@...gle.com Cc: xuyu@...ux.alibaba.com, akpm@...ux-foundation.org, mgorman@...e.de, aarcange@...hat.com, willy@...radead.org, linux-kernel@...r.kernel.org, kernel-team@...com, linux-mm@...ck.org, mhocko@...e.com Subject: Re: [PATCH 3/3] mm,thp,shmem: make khugepaged obey tmpfs mount flags On 11/26/20 7:14 PM, Rik van Riel wrote: > On Thu, 2020-11-26 at 18:18 +0100, Vlastimil Babka wrote: >> On 11/24/20 8:49 PM, Rik van Riel wrote: >>> Currently if thp enabled=[madvise], mounting a tmpfs filesystem >>> with huge=always and mmapping files from that tmpfs does not >>> result in khugepaged collapsing those mappings, despite the >>> mount flag indicating that it should. >>> >>> Fix that by breaking up the blocks of tests in hugepage_vma_check >>> a little bit, and testing things in the correct order. >>> >>> Signed-off-by: Rik van Riel <riel@...riel.com> >>> Fixes: c2231020ea7b ("mm: thp: register mm for khugepaged when >>> merging vma for shmem") >> >> Looks ok. But, it we have sysfs thp enabled=never, and shmem mount >> explicitly >> thp enabled, then shmem mount overrides the global sysfs setting and >> thp's will >> be allocated there, right? However, khugepaged_enabled() will be >> false and thus >> khugepaged won't run at all? So a similar situation than what you're >> fixing here. > > Indeed, that is somewhat similar. Whether or not shmem > allocations attempt huge pages is controlled by both > the file /sys/kernel/mm/transparent_hugepage/shmem_enabled Ah right, there's also that sysfs file. > and mount options. > > This patch makes khugepaged treat the mount options > and/or > sysfs flag as enabling collapsing of huge pages in case > enabled = [always] for regular THPs. > > Should I send another patch on top > of this that causes > khugepaged to be enabled when regular THPs are disabled, > but shmem THPs are enabled in any way? I think it would make sense. Although it might involve counting thp-enabled shmem mounts and only run khugepaged when there are >0 of them.
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