From: Kiryl Shutsemau <kirill@shutemov.name>
To: Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@meta.com, Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
"Liam R . Howlett" <liam@infradead.org>,
Nico Pache <nico.pache@linux.dev>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>, Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
Vlastimil Babka <vbabka@kernel.org>, Jann Horn <jannh@google.com>,
"Kiryl Shutsemau (Meta)" <kas@kernel.org>
Subject: [PATCH 01/12] mm/khugepaged: drop redundant mm_struct pin in madvise_collapse()
Date: Fri, 4 Sep 2026 16:10:15 +0100 [thread overview]
Message-ID: <1ff754df1d57154e01356f35d72b1cb06c0f8664.1788533997.git.kas@kernel.org> (raw)
In-Reply-To: <cover.1788533997.git.kas@kernel.org>
From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
madvise_collapse() holds an mmgrab() reference across its work. It is
redundant. Every caller already holds mm_users:
- madvise(2) works on current->mm, which lives as long as the task is in
the syscall;
- process_madvise(2) reaches a remote mm through mm_access(), which takes
an mm_users reference and holds it until the syscall returns;
- io_uring passes current->mm;
- DAMON takes one with get_task_mm() and drops it after the call.
Drop the mmgrab()/mmdrop() pair.
Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
mm/khugepaged.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index f49a6710933b..f1f8d4375e96 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -3236,7 +3236,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
cc->is_khugepaged = false;
cc->progress = 0;
- mmgrab(mm);
lru_add_drain_all();
for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
@@ -3292,7 +3291,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
}
out_nolock:
mmap_assert_locked(mm);
- mmdrop(mm);
kfree(cc);
return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0
--
2.54.0
next prev parent reply other threads:[~2026-09-04 15:10 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-04 15:10 [PATCH 00/12] mm/collapse: separate a collapse from its callers Kiryl Shutsemau
2026-09-04 15:10 ` Kiryl Shutsemau [this message]
2026-09-04 15:58 ` [PATCH 01/12] mm/khugepaged: drop redundant mm_struct pin in madvise_collapse() Zi Yan
2026-09-04 15:10 ` [PATCH 02/12] mm/khugepaged: count collapses where khugepaged makes them Kiryl Shutsemau
2026-09-05 2:25 ` Zi Yan
2026-09-04 15:10 ` [PATCH 03/12] mm/khugepaged: rename mthp_present_ptes bitmap to eligible_ptes Kiryl Shutsemau
2026-09-05 2:28 ` Zi Yan
2026-09-04 15:10 ` [PATCH 04/12] mm/collapse: add collapse.h for the collapse interface Kiryl Shutsemau
2026-09-05 2:36 ` Zi Yan
2026-09-04 15:10 ` [PATCH 05/12] mm/collapse: state what a collapse may do in the policy Kiryl Shutsemau
2026-09-05 2:44 ` Zi Yan
2026-09-04 15:10 ` [PATCH 06/12] mm/collapse: drop the collapse_possible() wrapper Kiryl Shutsemau
2026-09-05 2:45 ` Zi Yan
2026-09-04 15:10 ` [PATCH 07/12] mm/collapse: name the per-table scan reset for what it resets Kiryl Shutsemau
2026-09-05 18:05 ` Zi Yan
2026-09-04 15:10 ` [PATCH 08/12] mm/collapse: separate scanning a PTE table from collapsing it Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 09/12] mm/collapse: open-code collapse_single_pmd() in its two callers Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 10/12] mm/collapse: work out the orders a VMA allows once per VMA Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 11/12] mm/collapse: declare the collapse interface in collapse.h Kiryl Shutsemau
2026-09-04 15:10 ` [PATCH 12/12] mm/collapse: implement MADV_COLLAPSE in madvise.c Kiryl Shutsemau
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=1ff754df1d57154e01356f35d72b1cb06c0f8664.1788533997.git.kas@kernel.org \
--to=kirill@shutemov.name \
--cc=akpm@linux-foundation.org \
--cc=baohua@kernel.org \
--cc=baolin.wang@linux.alibaba.com \
--cc=david@kernel.org \
--cc=dev.jain@arm.com \
--cc=jannh@google.com \
--cc=kas@kernel.org \
--cc=kernel-team@meta.com \
--cc=lance.yang@linux.dev \
--cc=liam@infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=ljs@kernel.org \
--cc=nico.pache@linux.dev \
--cc=ryan.roberts@arm.com \
--cc=usama.arif@linux.dev \
--cc=vbabka@kernel.org \
--cc=ziy@nvidia.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
all inboxes | Powered by JetHome®