From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E22403EC2E6 for ; Tue, 14 Apr 2026 15:43:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776181418; cv=none; b=iih4UFcN73A8MmuSKoDAtsTiNW56r7Zb9boZv0nuWim0bz6irBaPnnLbsAbovTWDwnutYHdfpe+tgOGV5+gKyOmHbz7x0XYCuMkXn8Qd8VW/1Mwxgr15riMU9gGZbLjH7ZKD1YpFkVHe6y/YU3n1P9fRbGvHgmDi/QRLBrjvDs4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776181418; c=relaxed/simple; bh=hZDJpf0SiekVMU9h5Mt5tAfgMY1esUFBXHQ1y03LU4s=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=Bjs+8EMMBCL52NY7hkxGFbCF7kK6hXb5MNJSOPD402IZNRizN8iHVVX/NkcRtg4sIb29jRdKAUOqerg9SFgMnkRSpxZ3+ABpl5Zg6aG6o7bSOZ1UsO0rF1vRLnz5HNufeXDl/rdQzYLBDEBijrHcPQMMQqB0Gj+vSaBEd438ZjQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=a+Zoy3/H; arc=none smtp.client-ip=91.218.175.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="a+Zoy3/H" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1776181404; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xofRIGZTZWakFR4r7hnHb6VQphFQ4wt9gOLnTsomTno=; b=a+Zoy3/HP0If3I2KC+z/xy+o4Zd3PZ4Kc0jqpMBHxJwT2FNA1df/rmFfyx81rcasSH+5Hv 3D8TW/roWmTFaZKQaN7FwnaCG0eCBFeUrBT5hmsEqIkTCywMek5EgN3BWqJqRa7+KXE8dh ISMIBMFQ06zz7nJpwbC5FH7qif4qJk0= From: Lance Yang To: ziy@nvidia.com, david@kernel.org Cc: willy@infradead.org, songliubraving@fb.com, clm@fb.com, dsterba@suse.com, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, akpm@linux-foundation.org, ljs@kernel.org, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shuah@kernel.org, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Lance Yang Subject: Re: [PATCH 7.2 v2 01/12] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check Date: Tue, 14 Apr 2026 23:43:16 +0800 Message-Id: <20260414154316.42935-1-lance.yang@linux.dev> In-Reply-To: <20260414153724.35950-1-lance.yang@linux.dev> References: <20260414153724.35950-1-lance.yang@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On Tue, Apr 14, 2026 at 11:37:24PM +0800, Lance Yang wrote: > >On Tue, Apr 14, 2026 at 12:29:04PM +0200, David Hildenbrand (Arm) wrote: >>On 4/13/26 21:20, Zi Yan wrote: >>> collapse_file() requires FSes supporting large folio with at least >>> PMD_ORDER, so replace the READ_ONLY_THP_FOR_FS check with that. >>> MADV_COLLAPSE ignores shmem huge config, so exclude the check for shmem. >>> >>> While at it, replace VM_BUG_ON with VM_WARN_ON_ONCE. >>> >>> In collapse_scan_file(), add FS eligibility check to avoid redundant scans. >>> >>> Signed-off-by: Zi Yan >>> --- >>> mm/khugepaged.c | 12 ++++++++++-- >>> 1 file changed, 10 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>> index b8452dbdb043..d2f0acd2dac2 100644 >>> --- a/mm/khugepaged.c >>> +++ b/mm/khugepaged.c >>> @@ -1892,8 +1892,9 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, >>> int nr_none = 0; >>> bool is_shmem = shmem_file(file); >>> >>> - VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); >>> - VM_BUG_ON(start & (HPAGE_PMD_NR - 1)); >>> + /* MADV_COLLAPSE ignores shmem huge config, so do not check shmem */ >>> + VM_WARN_ON_ONCE(!is_shmem && mapping_max_folio_order(mapping) < PMD_ORDER); >>> + VM_WARN_ON_ONCE(start & (HPAGE_PMD_NR - 1)); >>> >>> result = alloc_charge_folio(&new_folio, mm, cc); >>> if (result != SCAN_SUCCEED) >>> @@ -2321,6 +2322,13 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, >>> int node = NUMA_NO_NODE; >>> enum scan_result result = SCAN_SUCCEED; >>> >>> + /* >>> + * skip files without PMD-order folio support >>> + * do not check shmem, since MADV_COLLAPSE ignores shmem huge config >>> + */ >> >>How is the !collapse path handled? Through thp_vma_allowable_order() in >>collapse_scan_mm_slot()? >> >>Wouldn't it be better to have that check exactly there? > >Right! Looks like patch #03[1] already does that, as David also pointed >out there :) > >With that in place, regular files should end up in file_thp_enabled(), >which checks that mapping_max_folio_order() >= PMD_ORDER. Forgot to add: thp_vma_allowable_order() -> file_thp_enabled() -> mapping_max_folio_order() check >For khugepaged, collapse_scan_mm_slot() calls thp_vma_allowable_order() >before entering the per-PMD scan loop, so ineligible regular file VMAs >should already get filtered there. > >madvise_collapse() also calls thp_vma_allowable_order() early, so it >should get the same filtering before reaching collapse_scan_file(). > >So the extra check here looks redundant :) > >[1] https://lore.kernel.org/linux-mm/20260413192030.3275825-4-ziy@nvidia.com/ > >Cheers, >Lance >