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Wed, 29 Apr 2026 07:05:00 -0700 (PDT) Received: from vini ([2401:4900:8fcb:3097:5ced:f23a:32ed:4b52]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-834ed6de621sm2803027b3a.29.2026.04.29.07.04.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Apr 2026 07:05:00 -0700 (PDT) From: Vineet Agarwal 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 Subject: [PATCH] mm/khugepaged: return -EAGAIN for SCAN_PAGE_HAS_PRIVATE in MADV_COLLAPSE Date: Wed, 29 Apr 2026 19:34:34 +0530 Message-ID: <20260429140434.439456-1-agarwal.vineet2006@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 --- 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