From: Xu Yu <xuyu@linux.alibaba.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, hughd@google.com
Cc: akpm@linux-foundation.org, gavin.dg@linux.alibaba.com
Subject: [PATCH v2] mm, thp: use head page in __migration_entry_wait
Date: Tue, 8 Jun 2021 17:22:39 +0800 [thread overview]
Message-ID: <b9836c1dd522e903891760af9f0c86a2cce987eb.1623144009.git.xuyu@linux.alibaba.com> (raw)
We notice that hung task happens in a conner but practical scenario when
CONFIG_PREEMPT_NONE is enabled, as follows.
Process 0 Process 1 Process 2..Inf
split_huge_page_to_list
unmap_page
split_huge_pmd_address
__migration_entry_wait(head)
__migration_entry_wait(tail)
remap_page (roll back)
remove_migration_ptes
rmap_walk_anon
cond_resched
Where __migration_entry_wait(tail) is occurred in kernel space, e.g.,
copy_to_user in fstat, which will immediately fault again without
rescheduling, and thus occupy the cpu fully.
When there are too many processes performing __migration_entry_wait on
tail page, remap_page will never be done after cond_resched.
This makes __migration_entry_wait operate on the compound head page,
thus waits for remap_page to complete, whether the THP is split
successfully or roll back.
Note that put_and_wait_on_page_locked helps to drop the page reference
acquired with get_page_unless_zero, as soon as the page is on the wait
queue, before actually waiting. So splitting the THP is only prevented
for a brief interval.
Fixes: ba98828088ad ("thp: add option to setup migration entries during PMD split")
Suggested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Gang Deng <gavin.dg@linux.alibaba.com>
Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
---
mm/migrate.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/mm/migrate.c b/mm/migrate.c
index b234c3f3acb7..41ff2c9896c4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -295,6 +295,7 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
goto out;
page = migration_entry_to_page(entry);
+ page = compound_head(page);
/*
* Once page cache replacement of page migration started, page_count
--
2.20.1.2432.ga663e714
next reply other threads:[~2021-06-08 9:22 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-08 9:22 Xu Yu [this message]
2021-06-08 12:00 ` [PATCH v2] mm, thp: use head page in __migration_entry_wait Kirill A. Shutemov
2021-06-08 12:32 ` Matthew Wilcox
2021-06-08 12:58 ` Kirill A. Shutemov
2021-06-08 13:35 ` Matthew Wilcox
2021-06-09 9:59 ` Kirill A. Shutemov
2021-06-08 13:22 ` Yu Xu
2021-06-09 10:08 ` Kirill A. Shutemov
2021-06-08 20:00 ` Hugh Dickins
2021-06-08 20:00 ` Hugh Dickins
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=b9836c1dd522e903891760af9f0c86a2cce987eb.1623144009.git.xuyu@linux.alibaba.com \
--to=xuyu@linux.alibaba.com \
--cc=akpm@linux-foundation.org \
--cc=gavin.dg@linux.alibaba.com \
--cc=hughd@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.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.