From: Matthew Wilcox <willy@infradead.org>
To: Yang Shi <shy828301@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Song Liu <songliubraving@fb.com>, Rik van Riel <riel@surriel.com>,
Zi Yan <ziy@nvidia.com>, Theodore Ts'o <tytso@mit.edu>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [v3 PATCH 0/8] Make khugepaged collapse readonly FS THP more consistent
Date: Wed, 27 Apr 2022 21:58:50 +0100 [thread overview]
Message-ID: <YmmuivdOWcr46oNC@casper.infradead.org> (raw)
In-Reply-To: <CAHbLzkoWPN+ahrvu2JrvoDpf8J_QGR6Ug6BbPnC11C82Lb-NaA@mail.gmail.com>
On Mon, Apr 04, 2022 at 05:48:49PM -0700, Yang Shi wrote:
> When khugepaged collapses file THPs, its behavior is not consistent.
> It is kind of "random luck" for khugepaged to see the file vmas (see
> report: https://lore.kernel.org/linux-mm/00f195d4-d039-3cf2-d3a1-a2c88de397a0@suse.cz/)
> since currently the vmas are registered to khugepaged when:
> - Anon huge pmd page fault
> - VMA merge
> - MADV_HUGEPAGE
> - Shmem mmap
>
> If the above conditions are not met, even though khugepaged is enabled
> it won't see any file vma at all. MADV_HUGEPAGE could be specified
> explicitly to tell khugepaged to collapse this area, but when
> khugepaged mode is "always" it should scan suitable vmas as long as
> VM_NOHUGEPAGE is not set.
I don't see that as being true at all. The point of this hack was that
applications which really knew what they were doing could enable it.
It makes no sense to me that setting "always" by the sysadmin for shmem
also force-enables ROTHP, even for applications which aren't aware of it.
Most telling, I think, is that Song Liu hasn't weighed in on this at
all. It's clearly not important to the original author.
next prev parent reply other threads:[~2022-04-27 20:59 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-04 20:02 Yang Shi
2022-04-04 20:02 ` [v3 PATCH 1/8] sched: coredump.h: clarify the use of MMF_VM_HUGEPAGE Yang Shi
2022-05-09 12:25 ` Vlastimil Babka
2022-04-04 20:02 ` [v3 PATCH 2/8] mm: khugepaged: remove redundant check for VM_NO_KHUGEPAGED Yang Shi
2022-05-09 12:45 ` Vlastimil Babka
2022-04-04 20:02 ` [v3 PATCH 3/8] mm: khugepaged: skip DAX vma Yang Shi
2022-05-09 12:46 ` Vlastimil Babka
2022-04-04 20:02 ` [v3 PATCH 4/8] mm: thp: only regular file could be THP eligible Yang Shi
2022-05-09 13:41 ` Vlastimil Babka
2022-04-04 20:02 ` [v3 PATCH 5/8] mm: khugepaged: make khugepaged_enter() void function Yang Shi
2022-05-09 13:46 ` Vlastimil Babka
2022-04-04 20:02 ` [v3 PATCH 6/8] mm: khugepaged: move some khugepaged_* functions to khugepaged.c Yang Shi
2022-05-09 15:31 ` Vlastimil Babka
2022-05-09 23:00 ` Yang Shi
2022-04-04 20:02 ` [v3 PATCH 7/8] mm: khugepaged: introduce khugepaged_enter_vma() helper Yang Shi
2022-05-09 15:39 ` Vlastimil Babka
2022-04-04 20:02 ` [v3 PATCH 8/8] mm: mmap: register suitable readonly file vmas for khugepaged Yang Shi
2022-05-09 15:43 ` Vlastimil Babka
2022-04-05 0:16 ` [v3 PATCH 0/8] Make khugepaged collapse readonly FS THP more consistent Matthew Wilcox
2022-04-05 0:48 ` Yang Shi
2022-04-27 20:58 ` Matthew Wilcox [this message]
2022-04-27 22:38 ` Yang Shi
2022-04-27 23:16 ` Yang Shi
2022-05-09 16:05 ` Vlastimil Babka
2022-05-09 20:34 ` Yang Shi
2022-05-10 7:35 ` Vlastimil Babka
2022-05-10 19:25 ` Yang Shi
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