From: Vineet Agarwal <agarwal.vineet2006@gmail.com>
To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, ziy@nvidia.com,
	baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com,
	npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com,
	baohua@kernel.org, lance.yang@linux.dev,
	Vineet Agarwal <agarwal.vineet2006@gmail.com>
Subject: [PATCH] mm/khugepaged: return -EAGAIN for SCAN_PAGE_HAS_PRIVATE in MADV_COLLAPSE
Date: Wed, 29 Apr 2026 19:34:34 +0530	[thread overview]
Message-ID: <20260429140434.439456-1-agarwal.vineet2006@gmail.com> (raw)

MADV_COLLAPSE uses errno values to provide actionable feedback to
userspace. Temporary resource constraints are mapped to -EAGAIN so the
caller may retry, while intrinsic failures of the specified range are
mapped to -EINVAL.

collapse_file() returns SCAN_PAGE_HAS_PRIVATE when
filemap_release_folio() fails while isolating file-backed folios for
collapse. This currently falls through the default case in
madvise_collapse_errno() and is reported to userspace as -EINVAL.

However, filemap_release_folio() failure commonly reflects temporary
folio state rather than a permanently uncollapsible range.

For example, ext4 returns false when a folio still has dirty
journalled data, btrfs returns false for dirty or writeback folios
before extent state release, and NFS may return false while reclaiming
filesystem-private folio state.

In such cases, retrying MADV_COLLAPSE after writeback, reclaim or
journal progress may succeed. This matches the existing -EAGAIN
handling for SCAN_PAGE_DIRTY_OR_WRITEBACK and other transient collapse
failures more closely than -EINVAL.

Therefore, map SCAN_PAGE_HAS_PRIVATE to -EAGAIN so userspace receives
retryable feedback for this temporary failure path.

Signed-off-by: Vineet Agarwal <agarwal.vineet2006@gmail.com>
---
 mm/khugepaged.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b8452dbdb043..58f55115d7d8 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2808,6 +2808,7 @@ static int madvise_collapse_errno(enum scan_result r)
 	case SCAN_PAGE_LRU:
 	case SCAN_DEL_PAGE_LRU:
 	case SCAN_PAGE_FILLED:
+	case SCAN_PAGE_HAS_PRIVATE:
 	case SCAN_PAGE_DIRTY_OR_WRITEBACK:
 		return -EAGAIN;
 	/*
-- 
2.54.0

next             reply	other threads:[~2026-04-29 14:05 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-04-29 14:04 Vineet Agarwal [this message]
2026-04-29 14:20 ` [PATCH] mm/khugepaged: return -EAGAIN for SCAN_PAGE_HAS_PRIVATE in MADV_COLLAPSE Dev Jain
2026-04-29 14:40   ` David Hildenbrand (Arm)
2026-04-29 14:57 ` Andrew Morton

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=20260429140434.439456-1-agarwal.vineet2006@gmail.com \
    --to=agarwal.vineet2006@gmail.com \
    --cc=Liam.Howlett@oracle.com \
    --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=lance.yang@linux.dev \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=ljs@kernel.org \
    --cc=npache@redhat.com \
    --cc=ryan.roberts@arm.com \
    --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

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.