From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-118.freemail.mail.aliyun.com (out30-118.freemail.mail.aliyun.com [115.124.30.118]) (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 2A0F613B5A9 for ; Fri, 5 Jul 2024 08:58:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.118 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720169887; cv=none; b=uSI/sFU2pZO3tEZE8q2WtpTzPawi3Sz8pcj5SxQtvufW6zR/SGhLEocV3mJ46+sr1odb2I1W3NCv5OP25qm8d3LKqwBjwpdwuJLUVh7ocO9M867REJN93838lxHwisn/VM6rBZI4emM6CcdH64i6ckTR5wlSHAKj5K9N/dyveDE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720169887; c=relaxed/simple; bh=hvG0GCOWi4THCguOysp1g8/zVPa9vVrWs5MMxbroZr0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eUm8+yE6AHABvnrt/dqbHpx0wL2ohtZ/B2iKwQNp5xi281ePuIzQNusVAhDKPxY9aGHVDCL7QpdV3k3MMJXcpAFX48Mx31lGHqxCT/qRQ3+GUItcKgLy3cywruQd4LsUyJ0y+Zai1aIsuplBYgrzf/t8NJIowmwJFDrvD9TvoGE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=HROtLVqi; arc=none smtp.client-ip=115.124.30.118 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="HROtLVqi" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1720169882; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=/b2CH/0osx3Zqy3K9+ynEPiLNGlIv+mnOfWfcW761j4=; b=HROtLVqiFcztkybnJQzBQhgU8h0QYOx8V5M6m9TDB8qFhrHFolKOjaqP4ZxgEo+xkCqQwSqL24lUzL0jY4zUHgso7T02dkgOBymdL5rnKg9Eqeq8UklZeGfYFZdbozYcSFOM9To4wiHRfllA4oM5InNRGl/W+Trf5/QC2ckVVec= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045220184;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=16;SR=0;TI=SMTPD_---0W9uQFI._1720169879; Received: from 30.97.56.65(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W9uQFI._1720169879) by smtp.aliyun-inc.com; Fri, 05 Jul 2024 16:58:00 +0800 Message-ID: <545e23ab-e40a-4f13-8167-c9aa85a34b19@linux.alibaba.com> Date: Fri, 5 Jul 2024 16:57:59 +0800 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 v5 4/6] mm: shmem: add mTHP support for anonymous shmem To: Ryan Roberts , Bang Li , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, david@redhat.com, wangkefeng.wang@huawei.com, ying.huang@intel.com, 21cnbao@gmail.com, shy828301@gmail.com, ziy@nvidia.com, ioworker0@gmail.com, da.gomez@samsung.com, p.raghav@samsung.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <65796c1e72e51e15f3410195b5c2d5b6c160d411.1718090413.git.baolin.wang@linux.alibaba.com> <65c37315-2741-481f-b433-cec35ef1af35@arm.com> <475332ea-a80b-421c-855e-a663d1d5bfc7@linux.alibaba.com> <076550c4-0e8a-4344-9f8a-31ae9e1051b5@linux.alibaba.com> <96625631-ef7d-44a2-ad5f-f7beb64f0ed0@arm.com> From: Baolin Wang In-Reply-To: <96625631-ef7d-44a2-ad5f-f7beb64f0ed0@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/7/5 16:42, Ryan Roberts wrote: > On 05/07/2024 04:01, Baolin Wang wrote: >> >> >> On 2024/7/4 22:46, Bang Li wrote: >>> Hi Bao lin, >>> >>> On 2024/7/4 19:15, Baolin Wang wrote: >>>> >>>>>> + >>>>>> +    /* >>>>>> +     * Only allow inherit orders if the top-level value is 'force', which >>>>>> +     * means non-PMD sized THP can not override 'huge' mount option now. >>>>>> +     */ >>>>>> +    if (shmem_huge == SHMEM_HUGE_FORCE) >>>>>> +        return READ_ONCE(huge_shmem_orders_inherit); >>>>> >>>>> I vaguely recall that we originally discussed that trying to set 'force' on the >>>>> top level control while any per-size controls were set to 'inherit' would be an >>>>> error, and trying to set 'force' on any per-size control except the PMD-size >>>>> would be an error? >>>> >>>> Right. >>>> >>>>> I don't really understand this logic. Shouldn't we just be looking at the >>>>> per-size control settings (or the top-level control as a proxy for every >>>>> per-size control that has 'inherit' set)? >>>> >>>> ‘force’ will apply the huge orders for anon shmem and tmpfs, so now we only >>>> allow pmd-mapped THP to be forced. We should not look at per-size control >>>> settings for tmpfs now (mTHP for tmpfs will be discussed in future). >>>> >>>>> >>>>> Then for tmpfs, which doesn't support non-PMD-sizes yet, we just always use the >>>>> PMD-size control for decisions. >>>>> >>>>> I'm also really struggling with the concept of shmem_is_huge() existing along >>>>> side shmem_allowable_huge_orders(). Surely this needs to all be refactored into >>>>> shmem_allowable_huge_orders()? >>>> >>>> I understood. But now they serve different purposes: shmem_is_huge() will be >>>> used to check the huge orders for the top level, for *tmpfs* and anon shmem; >>>> whereas shmem_allowable_huge_orders() will only be used to check the per-size >>>> huge orders for anon shmem (excluding tmpfs now). However, as I plan to add >>>> mTHP support for tmpfs, I think we can perform some cleanups. >>> >>> Please count me in, I'd be happy to contribute to the cleanup and enhancement >>> process if I can. >> >> Good. If you have time, I think you can look at the shmem khugepaged issue from >> the previous discussion [1], which I don't have time to look at now. >> >> " >> (3) khugepaged >> >> khugepaged needs to handle larger folios properly as well. Until fixed, >> using smaller THP sizes as fallback might prohibit collapsing a >> PMD-sized THP later. But really, khugepaged needs to be fixed to handle >> that. >> " > > khugepaged can already collapse "folios of any order less then PMD-size" to > PMD-size, for anon memory. Infact I modified the selftest to be able to test > that in commit 9f0704eae8a4 ("selftests/mm/khugepaged: enlighten for multi-size > THP"). I'd be surprised if khugepaged can't alreay handle the same for shmem? I did not test this, but from the comment in hpage_collapse_scan_file(), seems that compacting small mTHP into a single PMD-mapped THP is not supported yet. /* * TODO: khugepaged should compact smaller compound pages * into a PMD sized page */ if (folio_test_large(folio)) { result = folio_order(folio) == HPAGE_PMD_ORDER && folio->index == start /* Maybe PMD-mapped */ ? SCAN_PTE_MAPPED_HUGEPAGE : SCAN_PAGE_COMPOUND; /* * For SCAN_PTE_MAPPED_HUGEPAGE, further processing * by the caller won't touch the page cache, and so * it's safe to skip LRU and refcount checks before * returning. */ break; } > Although the test will definitely want to be extended to test it. Right.