From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 8225D2BD5A8 for ; Fri, 24 Jul 2026 15:01:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784905262; cv=none; b=Jk8h7QYNF9Qja9MUmGSEwYnSLJ+wqEwQTY245T7+cbiMgLQECLzyCx+uRpaAfs9iSwR4JTh6GBRHb7NzxMAtikZ4vmAi44ecITdIKuGCQjcg5HVPtTRPiu8d+WZHK/hCZ4kuntJW/svB5uHyMyUlQaa1ta6++Vz1LIiWC5xOvo8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784905262; c=relaxed/simple; bh=MyihDH7eV4+mdocxLW1PQDdQuFmlswKLWM+blFaP7Rw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=G3zTOe5Gd7afRHWOzWYcDNUKQYFPpIW3XX4poBEtRcgXwhfbAR601A9uv7c3JC85zzkF5zIVP7x2C2pE8dXO2qjhVkwYRE44WCUeJJUENy6PCk6v+5nIBO0hYp4xMwOLxcEr7WaPjHJ1o+QVPd6HqvtDDXi2NmY7MdHpRqaasb8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=e8W6X5M2; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="e8W6X5M2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 874C11F000E9; Fri, 24 Jul 2026 15:00:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784905260; bh=kuWKgYJKiGV4VnZawJ+31C9x8fGlUZAxGdZ/7YC2SfQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=e8W6X5M2pWsGtZi5XaJpnWsvWT++ncbBXhDqFjs8KD0up2kycu/GMZbclBqiYBpSt wGzBMfmT23dSVR2aOyK3651NPXs6EiED71CrPgklCvktIgQIhU01/x2l2RJV32mRUb I61yvMTDXNEj8/Qnqjv/d5VsR3GZRx5THPnfMJJJST27AmgHSZXc+e0Y0wb7c+q2i1 0QmyTiTnRi3iUuGrsUSWf21jiNgRfMYLqSo8x/i9HorgD9ELZuNaXx51c0diW3/Yv5 znuxqK3yOKhTHRPlenaKzAkp2IxQCW6Xev/WewcVy0CG5AMyMXyRrCxf3PLIVE2EO7 ms5vOavVoI+lQ== Message-ID: <7b403326-b716-4766-9488-3bf662b74a64@kernel.org> Date: Fri, 24 Jul 2026 17:00:56 +0200 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/mlock: skip __mm_populate() for MLOCK_ONFAULT Content-Language: en-US To: "Lorenzo Stoakes (ARM)" , Wandun Chen Cc: liam@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, jannh@google.com, pfalcato@suse.de References: <20260722125133.543441-1-chenwandun1@gmail.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/22/26 14:59, Lorenzo Stoakes (ARM) wrote: > On Wed, Jul 22, 2026 at 08:51:33PM +0800, Wandun Chen wrote: >> From: Wandun Chen >> >> MLOCK_ONFAULT only locks pages on future faults, so there is no need to >> fault in non-present pages during the mlock2/mlockall syscall. >> populate_vma_page_range() already returns immediately for VMAs with >> VM_LOCKONFAULT, which means __mm_populate() just loops over VMAs and >> holds mmap_read_lock without doing useful work. >> >> Skip __mm_populate() when MLOCK_ONFAULT is set to avoid this unnecessary >> work. >> >> Signed-off-by: Wandun Chen > > Well you take mmap read lock and release it (after having held the write lock), > hardly earth-shattering. > > And this has been this way for donkey's years I don't really see why we should > care? > > Do you have a workload that's heavily dependent on mlock2(..., MLOCK_ONFAULT) or > mlockall(..., MCL_ONFAULT) as a hot path that is seriously contending the mmap > lock? > > I don't love how the VMA_LOCKONFAULT_BIT flag works but I'm not sure adding more > churn and code for the sake of it here is really worth it. > > Thanks, Lorenzo While that's true, I don't see a problem taking the patch. Otherwise we'll have to keep rejecting all future attempts (including LLM) doing the same because it just seems like a low hanging fruit to stop doing an unnecessary thing. And it's not that much of a churn or new code, IMHO. >> --- >> mm/mlock.c | 10 ++++++---- >> 1 file changed, 6 insertions(+), 4 deletions(-) >> >> diff --git a/mm/mlock.c b/mm/mlock.c >> index efa6716e4dfb..784bd4bfc3bb 100644 >> --- a/mm/mlock.c >> +++ b/mm/mlock.c >> @@ -658,9 +658,11 @@ static __must_check int do_mlock(unsigned long start, size_t len, >> if (error) >> return error; >> >> - error = __mm_populate(start, len, 0); >> - if (error) >> - return __mlock_posix_error_return(error); >> + if (!vma_flags_test(flags, VMA_LOCKONFAULT_BIT)) { >> + error = __mm_populate(start, len, 0); >> + if (error) >> + return __mlock_posix_error_return(error); >> + } >> return 0; >> } >> >> @@ -778,7 +780,7 @@ SYSCALL_DEFINE1(mlockall, int, flags) >> capable(CAP_IPC_LOCK)) >> ret = apply_mlockall_flags(flags); >> mmap_write_unlock(current->mm); >> - if (!ret && (flags & MCL_CURRENT)) >> + if (!ret && (flags & MCL_CURRENT) && !(flags & MCL_ONFAULT)) >> mm_populate(0, TASK_SIZE); >> >> return ret; >> -- >> 2.43.0 >>