From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta0.migadu.com (out-171.mta0.migadu.com [91.218.175.171]) (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 CED68333745 for ; Tue, 14 Apr 2026 15:37:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776181070; cv=none; b=q5ulse/Rx3b+gp2nDduhxm1jk9C9rplAZF8ieOiRLdQDLtq07+CateuB2j8iwVWPztnlVsEXzdkhA2Ih5Mf2vTYtnf1pCGNLspcyOOihiyxSTKdIcfxC9fbZqyhxntUytycgCEKWtfL+8ux2IDj7Pl4vD1NGF4PRYL4h2X0CSQY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776181070; c=relaxed/simple; bh=1qho8223zo/i33FqA9GXNiIckrugCgRh54ZzVLSY51A=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=ZrjjsnJMj4QceK7TUJCVcKSW07S/1f0GeoAZyg5viUmQ+so2T3Zu5U+WBEuoZY1veYXSfn1K91RzvVyN3qon/1swBYg8swA9H+fKhAWQ+y7Bwyw+M3oMHeBCSpi3oO7cbSSXOuAw6MNEZL0WHP18bQQOHTJ9xvIHWynd8Bl9rRw= 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=lAGKQfzg; arc=none smtp.client-ip=91.218.175.171 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="lAGKQfzg" 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=1776181055; 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=m1TDAGgzmOk8H25UKOcIJUxhIEuJydpP4AYeIgjDbV4=; b=lAGKQfzgeioiew63mH3E5n+R9eC1bKNYhY1BlrajddJgdTLtmQ+SiAx0mv0jnamulB/1aj fBWttHSarXPes6jFjVQVGNOlcwl6F2y26bDpQGPgdg4yq9BE7BsqWIynXleZNk8qemiG46 L1j3NTnooylL4ejFk0HNXT7EkZrFaAU= From: Lance Yang To: david@kernel.org, ziy@nvidia.com 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, lance.yang@linux.dev, 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 Subject: Re: [PATCH 7.2 v2 01/12] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check Date: Tue, 14 Apr 2026 23:37:24 +0800 Message-Id: <20260414153724.35950-1-lance.yang@linux.dev> In-Reply-To: References: 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 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. 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