From: Baolin Wang <baolin.wang@linux.alibaba.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] mm: migrate: Move the page count validation to the proper place
Date: Sun, 8 Aug 2021 10:55:30 +0800 [thread overview]
Message-ID: <36956352-246a-b3c2-3ade-2a6c22e2cd5a@linux.alibaba.com> (raw)
In-Reply-To: <YQ3puWSgUvfvIYjv@casper.infradead.org>
Hi,
> On Fri, Aug 06, 2021 at 11:07:18AM +0800, Baolin Wang wrote:
>> Hi Matthew,
>>
>>> On Thu, Aug 05, 2021 at 11:05:56PM +0800, Baolin Wang wrote:
>>>> We've got the expected count for anonymous page or file page by
>>>> expected_page_refs() at the beginning of migrate_page_move_mapping(),
>>>> thus we should move the page count validation a little forward to
>>>> reduce duplicated code.
>>>
>>> Please add an explanation to the changelog for why it's safe to pull
>>> this out from under the i_pages lock.
>>
>> Sure. In folio_migrate_mapping(), we are sure that the migration page was
>> isolated from lru list and locked, so I think there are no race to get the
>> page count without i_pages lock. Please correct me if I missed something
>> else. Thanks.
>
> Unless the page has been removed from i_pages, this isn't a correct
> explanation. Even if it has been removed from i_pages, unless an
> RCU grace period has passed, another CPU may still be able to inc the
> refcount on it (temporarily). The same is true for the page tables,
> by the way; if someone is using get_user_pages_fast(), they may still
> be able to see the page.
I don't think this is an issue, cause now we've established a migration
pte for this migration page under page lock. If the user want to get
page by get_user_pages_fast(), it will wait for the page miggration
finished by migration_entry_wait(). So I still think there is no need to
check the migration page count under the i_pages lock.
next prev parent reply other threads:[~2021-08-08 2:55 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-05 15:05 [PATCH 0/5] Some cleanup for page migration Baolin Wang
2021-08-05 15:05 ` [PATCH 1/5] mm: migrate: Move the page count validation to the proper place Baolin Wang
2021-08-05 15:17 ` Matthew Wilcox
2021-08-06 3:07 ` Baolin Wang
2021-08-07 2:02 ` Matthew Wilcox
2021-08-08 2:55 ` Baolin Wang [this message]
2021-08-08 10:26 ` Matthew Wilcox
2021-08-08 15:13 ` Baolin Wang
2021-08-08 16:01 ` Matthew Wilcox
2021-08-09 4:19 ` Baolin Wang
2021-08-05 15:05 ` [PATCH 2/5] mm: migrate: Introduce a local variable to get the number of pages Baolin Wang
2021-08-05 17:42 ` Yang Shi
2021-08-05 17:42 ` Yang Shi
2021-08-05 15:05 ` [PATCH 3/5] mm: migrate: Fix the incorrect function name in comments Baolin Wang
2021-08-05 17:26 ` Yang Shi
2021-08-05 17:26 ` Yang Shi
2021-08-09 13:59 ` Alistair Popple
2021-08-05 15:05 ` [PATCH 4/5] mm: migrate: Change to use bool type for 'page_was_mapped' Baolin Wang
2021-08-05 17:34 ` Yang Shi
2021-08-05 17:34 ` Yang Shi
2021-08-05 15:06 ` [PATCH 5/5] mm: migrate: Remove redundant goto labels Baolin Wang
2021-08-05 19:54 ` Yang Shi
2021-08-05 19:54 ` Yang Shi
2021-08-06 3:20 ` Baolin Wang
2021-08-06 17:17 ` Yang Shi
2021-08-06 17:17 ` Yang Shi
2021-08-08 2:56 ` Baolin Wang
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=36956352-246a-b3c2-3ade-2a6c22e2cd5a@linux.alibaba.com \
--to=baolin.wang@linux.alibaba.com \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=willy@infradead.org \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.