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 F2BED22ACEF for ; Mon, 6 Oct 2025 04:48:15 +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=1759726099; cv=none; b=DRzFwwYS0GMeblCoy7ItA0eUAzU/TjtPRJryVpdrqAUjcHRNsXEB7aOXN8loi4gY4gdsq8+FQBmR2mFYO0pmyrmRb781+0TSYE54mvjuIBsRaNyN5ZQdqlBZ0X4BEhuKVJRqcRban+L2iiq70je4anY8yLCH9TPuJW4zDgWdUso= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759726099; c=relaxed/simple; bh=WR5z416GdyHVMtZv8PL/xhfJeDMKBMQyDzp3mXaNyaQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GlMC9Pd+1vviL13gPaP44inkCd/H07QJSRXTVMHw55JgB96sUmFA4uiQh8tDGJ9kcYHkeVbBZdC74vEEBz7fD5ntJzLdjODQaLLHXsPKFWHL/Fz9NXbgShZga0FBhtCEmj5JNmw01MyH/60kejNfpkDyPsHnETbLnGWSRsHwRDA= 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; 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 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 30E551516; Sun, 5 Oct 2025 21:48:07 -0700 (PDT) Received: from [10.163.66.9] (unknown [10.163.66.9]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B81953F59E; Sun, 5 Oct 2025 21:48:12 -0700 (PDT) Message-ID: <3c0169a4-78b3-4deb-b991-14733b5f0aff@arm.com> Date: Mon, 6 Oct 2025 10:18:08 +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 v2] mm: readahead: make thp readahead conditional to mmap_miss logic To: Roman Gushchin , Andrew Morton Cc: linux-kernel@vger.kernel.org, Jan Kara , "Matthew Wilcox (Oracle)" , linux-mm@kvack.org References: <20251006015409.342697-1-roman.gushchin@linux.dev> Content-Language: en-US From: Dev Jain In-Reply-To: <20251006015409.342697-1-roman.gushchin@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 06/10/25 7:24 am, Roman Gushchin wrote: > Commit 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file mappings") > introduced a special handling for VM_HUGEPAGE mappings: even if the > readahead is disabled, 1 or 2 HPAGE_PMD_ORDER pages are > allocated. > > This change causes a significant regression for containers with a > tight memory.max limit, if VM_HUGEPAGE is widely used. Prior to this > commit, mmap_miss logic would eventually lead to the readahead > disablement, effectively reducing the memory pressure in the > cgroup. With this change the kernel is trying to allocate 1-2 huge > pages for each fault, no matter if these pages are used or not > before being evicted, increasing the memory pressure multi-fold. > > To fix the regression, let's make the new VM_HUGEPAGE conditional > to the mmap_miss check, but keep independent from the ra->ra_pages. > This way the main intention of commit 4687fdbb805a ("mm/filemap: > Support VM_HUGEPAGE for file mappings") stays intact, but the > regression is resolved. > > The logic behind this changes is simple: even if a user explicitly > requests using huge pages to back the file mapping (using VM_HUGEPAGE > flag), under a very strong memory pressure it's better to fall back > to ordinary pages. > > Signed-off-by: Roman Gushchin > Reviewed-by: Jan Kara > Cc: Matthew Wilcox (Oracle) > Cc: Dev Jain > Cc: linux-mm@kvack.org > > -- > > v2: fixed VM_SEQ_READ handling (by Dev Jain) > As you said in a previous mail, we definitely need some other way of measuring memory pressure here. Since your workload is doing madvise(MADV_HUGEPAGE) (which means it expects to take advantage of the hugepage by accessing it frequently) and still getting lots of cache misses, I guess it must be due to swapping out due to tight memory.max. Anyways, the change looks correct to me. Reviewed-by: Dev Jain