linux-kernel - [PATCH V2 0/2] mm/khugepaged: fix dirty page handling for MADV

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Message-ID: <20251120065043.41738-6-shivankg@amd.com>
Date: Thu, 20 Nov 2025 06:50:46 +0000
From: Shivank Garg <shivankg@....com>
To: Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand
	<david@...nel.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
CC: Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>, Barry Song
	<baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>, Steven Rostedt
	<rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, "Mathieu
 Desnoyers" <mathieu.desnoyers@...icios.com>, Zach O'Keefe
	<zokeefe@...gle.com>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<linux-trace-kernel@...r.kernel.org>, Shivank Garg <shivankg@....com>
Subject: [PATCH V2 0/2] mm/khugepaged: fix dirty page handling for MADV_COLLAPSE

MADV_COLLAPSE on file-backed mappings fails with -EINVAL when TEXT pages
are dirty. This may affect real scenarios: package/container updates,
executing binaries immediately after writing them, etc.

The issue is that collapse_file() triggers async writeback and returns
SCAN_FAIL (maps to -EINVAL), expecting khugepaged to revisit later. But
MADV_COLLAPSE is synchronous and userspace expects immediate success or a
clear retry signal.

Reproduction:
 - Copy 2MB-aligned executable to freshly mounted XFS/ext4
 - Call MADV_COLLAPSE on .text section
 - First call fails with -EINVAL (text pages dirty from copy)
 - Second call succeeds (async writeback completed)

Issue Report:
https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@amd.com

v2:
- Move writeback to madvise_collapse() (better abstraction, proper
  mmap_lock handling and does VMA revalidation after I/O) (Lorenzo)
- Rename to SCAN_PAGE_DIRTY to SCAN_PAGE_NOT_CLEAN and extend its use
  for all dirty/writeback folio cases that previously returned incorrect
  results (Dev) 

v1: https://lore.kernel.org/all/20251110113254.77822-1-shivankg@amd.com

Shivank Garg (2):
  mm/khugepaged: do synchronous writeback for MADV_COLLAPSE
  mm/khugepaged: map dirty/writeback pages failures to EAGAIN

 include/trace/events/huge_memory.h |  3 ++-
 mm/khugepaged.c                    | 34 +++++++++++++++++++++++++++---
 2 files changed, 33 insertions(+), 4 deletions(-)


base-commit: 4a3f8fc3adb7046e44bd1feb2f5c5fe95296894f
-- 
2.43.0