From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 00BCF277C9D for ; Wed, 29 Apr 2026 14:20:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777472421; cv=none; b=q/Zu3kj4FQ0cnqWoMdriMccVQbXIKutDvolLao34+oZQbJE5qLtN6jwwvc+zVvY+48ZmlMmW7m1URV1DXi28uTwU+uk+6tFSR6e6FBv+PZ+IT2rU5eIhK2MqTNC0tJ6JiaKoUPvbOVkhyHkbieASfN4vz3okUs9vkxnXIuJzBAw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777472421; c=relaxed/simple; bh=yu/k00bXF4IsrPajU5vK3oy2hwcnNad/5yhRTlK/Gv4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YM8U8/+FPpWd9+23OPyovCZTrPMAbC6lTm3nLhjwviE1y0ehgNFOOnJVNX3qo129N1l74IEc108/QTnkdZ4hyKEAx2weZKFy64FvDtatckGJCzouMXKpOwXkZH+iJSe+l4CWtiaddUPLnTS3xkYW644CgQ544xzUbYudoZ4CJsU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=cAPLVnUU; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="cAPLVnUU" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D62C71BCB; Wed, 29 Apr 2026 07:20:13 -0700 (PDT) Received: from [10.164.148.40] (MacBook-Pro.blr.arm.com [10.164.148.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0B17F3F62B; Wed, 29 Apr 2026 07:20:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1777472419; bh=yu/k00bXF4IsrPajU5vK3oy2hwcnNad/5yhRTlK/Gv4=; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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