From: "Zach O'Keefe" <zokeefe@google.com>
To: linux-mm@kvack.org, Yang Shi <shy828301@gmail.com>
Cc: linux-kernel@vger.kernel.org,
Saurabh Singh Sengar <ssengar@microsoft.com>
Subject: Re: [PATCH] mm/thp: fix "mm: thp: kill __transhuge_page_enabled()"
Date: Sat, 12 Aug 2023 14:24:40 -0700 [thread overview]
Message-ID: <CAAa6QmQw+F=o6htOn=6ADD6mwvMO=Ow_67f3ifBv3GpXx9Xg_g@mail.gmail.com> (raw)
In-Reply-To: <20230812210053.2325091-1-zokeefe@google.com>
On Sat, Aug 12, 2023 at 2:01 PM Zach O'Keefe <zokeefe@google.com> wrote:
>
> The 6.0 commits:
>
> commit 9fec51689ff6 ("mm: thp: kill transparent_hugepage_active()")
> commit 7da4e2cb8b1f ("mm: thp: kill __transhuge_page_enabled()")
>
> merged "can we have THPs in this VMA?" logic that was previously done
> separately by fault-path, khugepaged, and smaps "THPeligible".
>
> During the process, the check on VM_NO_KHUGEPAGED from the khugepaged
> path was accidentally added to fault and smaps paths. Certainly the
> previous behavior for fault should be restored, and since smaps should
> report the union of THP eligibility for fault and khugepaged, also opt
> smaps out of this constraint.
>
> Fixes: 7da4e2cb8b1f ("mm: thp: kill __transhuge_page_enabled()")
> Reported-by: Saurabh Singh Sengar <ssengar@microsoft.com>
> Signed-off-by: Zach O'Keefe <zokeefe@google.com>
> Cc: Yang Shi <shy828301@gmail.com>
> ---
> mm/huge_memory.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index eb3678360b97..e098c26d5e2e 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -96,11 +96,11 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
> return in_pf;
>
> /*
> - * Special VMA and hugetlb VMA.
> + * khugepaged check for special VMA and hugetlb VMA.
> * Must be checked after dax since some dax mappings may have
> * VM_MIXEDMAP set.
> */
> - if (vm_flags & VM_NO_KHUGEPAGED)
> + if (!in_pf && !smaps && (vm_flags & VM_NO_KHUGEPAGED))
> return false;
>
> /*
> --
> 2.41.0.694.ge786442a9b-goog
>
I should note that this was discussed before[1], and VM_MIXEDMAP was
called out then, but we didn't have any use cases.
What was reported broken by Saurabh was an out-of-tree driver that
relies on being able to fault in THPs over VM_HUGEPAGE|VM_MIXEDMAP
VMAs. We mentioned back then we could always opt fault-path out of
this check in the future, and it seems like we should.
To that extent, should this be added to stable?
Apologies, I should have added this context to the commit log.
Best,
Zach
[1] https://lore.kernel.org/linux-mm/YqdPmitColnzlXJ0@google.com/
next prev parent reply other threads:[~2023-08-12 21:25 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-12 21:00 [PATCH] mm/thp: fix "mm: thp: kill __transhuge_page_enabled()" Zach O'Keefe
2023-08-12 21:24 ` Zach O'Keefe [this message]
2023-08-13 6:19 ` [EXTERNAL] " Saurabh Singh Sengar
2023-08-14 18:47 ` Zach O'Keefe
2023-08-14 19:06 ` Matthew Wilcox
2023-08-15 0:04 ` Zach O'Keefe
2023-08-15 2:24 ` Matthew Wilcox
2023-08-16 16:52 ` Saurabh Singh Sengar
2023-08-16 21:47 ` Zach O'Keefe
2023-08-17 17:46 ` Yang Shi
2023-08-17 18:29 ` Zach O'Keefe
2023-08-18 21:21 ` Yang Shi
2023-08-21 15:08 ` Zach O'Keefe
2023-08-21 22:59 ` Yang Shi
2023-08-16 21:31 ` Zach O'Keefe
2023-08-17 12:18 ` Matthew Wilcox
2023-08-17 18:13 ` Zach O'Keefe
2023-08-17 19:01 ` Matthew Wilcox
2023-08-17 21:12 ` Zach O'Keefe
2023-08-16 16:49 ` Saurabh Singh Sengar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAAa6QmQw+F=o6htOn=6ADD6mwvMO=Ow_67f3ifBv3GpXx9Xg_g@mail.gmail.com' \
--to=zokeefe@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=shy828301@gmail.com \
--cc=ssengar@microsoft.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).