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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=cAPLVnUUUAxNAGLsklYDcy5M5RAmUPtK0z2SgAS1C/tR0Zsh4UH4fBdR1Of0pldGd Ka/2ZlaOVUpOQnmDWA3lpc7HUXMV4qcVsk82Z+Jm7wVCAwXxJO28XKZoc5FBLA9k+F ITbDbvj6ky77TH/+gIvvJZiBmcedKkQUW428qTAE= Message-ID: <70b44146-4549-479f-8d31-b40a8e747c60@arm.com> Date: Wed, 29 Apr 2026 19:50:05 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/khugepaged: return -EAGAIN for SCAN_PAGE_HAS_PRIVATE in MADV_COLLAPSE To: Vineet Agarwal , 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, baohua@kernel.org, lance.yang@linux.dev References: <20260429140434.439456-1-agarwal.vineet2006@gmail.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20260429140434.439456-1-agarwal.vineet2006@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 33rs6751tbp94mccs8hh75fuqzd9cmni X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3D78840003 X-Rspam-User: X-HE-Tag: 1777472420-216163 X-HE-Meta: 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 0amx/VSF b3Cq+H+LZdtLI8qWVWhv+3olkV9K3E35LB5q4Flw6b6PytZeI3YS6mxFWvlsgfuwafwbvlsVaG9vxfeWHwaUVgB36j+FCZwqZdL669QSCRWPLLLonFS3Wb6p8VL4W2JidDdC2gJRRNe7/i2FPAmng+8uo06Ump0W6w+Rz3VcAA2LfyduEW2+8az2Q69pRFhuA4uA84CRuGOySAQQsniJNyKLSC2RYaZi/F/Eag1+FGjMKFFCdGR/OzGYFvfEY5aoBu+g2HyVSRb4EgKY9b/aW0wlUR3D+3MlEf31vtxZMzqdCVSD3JraKmuab6D/JeSkJ37mdBs4hv04nabtyIWGcDQ+FkMDtmOi7/iEyruZzaM8wJOH43vircg1xPQjfJbWkCyyJ5xH1Z4WvBkmkxY23II9NGlCj6tBxFGKBuasiwy9tiLduUDZ7oHkRDTf0OOqfsRrZ4vRIrHw5NJQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 29/04/26 7:34 pm, Vineet Agarwal wrote: > 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; > /* https://lore.kernel.org/all/4ab54ae0-2607-443d-8698-788d8e951bdd@arm.com/ I had mentioned at that time, other error codes may fit the -EAGAIN (or something else) definition as well, for example, probably SCAN_TRUNCATED. Could you please audit other error codes as well? Anyhow to your patch here: Reviewed-by: Dev Jain