From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com [115.124.30.131]) (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 7312C14D2B5 for ; Tue, 7 May 2024 09:33:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715074402; cv=none; b=RjJcArhce08pMEi98haSfqvdrpOgIG7Hrq0ne0LVR2H+BeTBqTSKUGVi9Vzr5Acd/5+c1KYir4Exf6mZYBLwAzGz11TYGvPjgY0jiAhn5CVgvi5qe7fJugyhZzVcZjdCOhARPM7V3OG50RxL7I5w5RxkQOzgCz5upeWTtC7uNS0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715074402; c=relaxed/simple; bh=BYzD9DZm8ky4zklZ02OGKg8jsfq4uW90exzTQmvJGm4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UhtS/rZ8mnq0XOG7nEBNsgo9Mkt4b2JpUWhYbZxSg8Xcc6zAWSrIWg2ZaAc/BOSssy389M6JpDaIBK7jrwDiOhBJPsFHvwidH0Bp4zfnjoCz7N0ILGF5XT2l7KKAgBDDbmgSrsGaRSX1/B9KPokZz+NHEDus+DUHQzKo6ZhwyL4= 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=pLrka0Lu; arc=none smtp.client-ip=115.124.30.131 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="pLrka0Lu" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1715074395; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=m+W6LCQqw+fad3DX5hnYaBtalOAck6XbEGLoiU/WMjY=; b=pLrka0LuW+Pzno6s/zhL5bcclGXXYknmnsKznRDR/3R0yvqs5oyRTdpfgcxDqtZbVbWnMz/KL2g/IyPDpnJ9lLBEHnadyW8JkvQ+0SKXwMHV6jcjiVtaaegEL3DPyqAMd6QOzyHDfTEm+nncytUzcmbrxlhuCpZfFgCdh/Mk6Bg= 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-contentspam033045046011;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=21;SR=0;TI=SMTPD_---0W6.oB1W_1715074391; Received: from 30.236.4.40(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W6.oB1W_1715074391) by smtp.aliyun-inc.com; Tue, 07 May 2024 17:33:12 +0800 Message-ID: <8c1d6e06-d84b-4be7-81c8-76e2d8fb9883@linux.alibaba.com> Date: Tue, 7 May 2024 17:33:11 +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 v4 3/3] mm/vmscan: avoid split lazyfree THP during shrink_folio_list() To: Lance Yang Cc: akpm@linux-foundation.org, willy@infradead.org, sj@kernel.org, maskray@google.com, ziy@nvidia.com, ryan.roberts@arm.com, david@redhat.com, 21cnbao@gmail.com, mhocko@suse.com, fengwei.yin@intel.com, zokeefe@google.com, shy828301@gmail.com, xiehuan09@gmail.com, libang.li@antgroup.com, wangkefeng.wang@huawei.com, songmuchun@bytedance.com, peterx@redhat.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240501042700.83974-1-ioworker0@gmail.com> <20240501042700.83974-4-ioworker0@gmail.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/5/7 16:26, Lance Yang wrote: > On Tue, May 7, 2024 at 2:32 PM Lance Yang wrote: >> >> Hey Baolin, >> >> Thanks a lot for taking time to review! >> >> On Tue, May 7, 2024 at 12:01 PM Baolin Wang >> wrote: >>> >>> >>> >>> On 2024/5/1 12:27, Lance Yang wrote: >>>> When the user no longer requires the pages, they would use >>>> madvise(MADV_FREE) to mark the pages as lazy free. Subsequently, they >>>> typically would not re-write to that memory again. >>>> >>>> During memory reclaim, if we detect that the large folio and its PMD are >>>> both still marked as clean and there are no unexpected references >>>> (such as GUP), so we can just discard the memory lazily, improving the >>>> efficiency of memory reclamation in this case. On an Intel i5 CPU, reclaiming 1GiB of lazyfree THPs using >>>> mem_cgroup_force_empty() results in the following runtimes in seconds >>>> (shorter is better): >>>> >>>> -------------------------------------------- >>>> | Old | New | Change | >>>> -------------------------------------------- >>>> | 0.683426 | 0.049197 | -92.80% | >>>> -------------------------------------------- >>>> >>>> Suggested-by: Zi Yan >>>> Suggested-by: David Hildenbrand >>>> Signed-off-by: Lance Yang >>>> --- >>>> include/linux/huge_mm.h | 9 +++++ >>>> mm/huge_memory.c | 73 +++++++++++++++++++++++++++++++++++++++++ >>>> mm/rmap.c | 3 ++ >>>> 3 files changed, 85 insertions(+) >>>> >>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>>> index 38c4b5537715..017cee864080 100644 >>>> --- a/include/linux/huge_mm.h >>>> +++ b/include/linux/huge_mm.h >>>> @@ -411,6 +411,8 @@ static inline bool thp_migration_supported(void) >>>> >>>> void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address, >>>> pmd_t *pmd, bool freeze, struct folio *folio); >>>> +bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, >>>> + pmd_t *pmdp, struct folio *folio); >>>> >>>> static inline void align_huge_pmd_range(struct vm_area_struct *vma, >>>> unsigned long *start, >>>> @@ -492,6 +494,13 @@ static inline void align_huge_pmd_range(struct vm_area_struct *vma, >>>> unsigned long *start, >>>> unsigned long *end) {} >>>> >>>> +static inline bool unmap_huge_pmd_locked(struct vm_area_struct *vma, >>>> + unsigned long addr, pmd_t *pmdp, >>>> + struct folio *folio) >>>> +{ >>>> + return false; >>>> +} >>>> + >>>> #define split_huge_pud(__vma, __pmd, __address) \ >>>> do { } while (0) >>>> >>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>> index 145505a1dd05..90fdef847a88 100644 >>>> --- a/mm/huge_memory.c >>>> +++ b/mm/huge_memory.c >>>> @@ -2690,6 +2690,79 @@ static void unmap_folio(struct folio *folio) >>>> try_to_unmap_flush(); >>>> } >>>> >>>> +static bool __discard_trans_pmd_locked(struct vm_area_struct *vma, >>>> + unsigned long addr, pmd_t *pmdp, >>>> + struct folio *folio) >>>> +{ >>>> + struct mm_struct *mm = vma->vm_mm; >>>> + int ref_count, map_count; >>>> + pmd_t orig_pmd = *pmdp; >>>> + struct mmu_gather tlb; >>>> + struct page *page; >>>> + >>>> + if (pmd_dirty(orig_pmd) || folio_test_dirty(folio)) >>>> + return false; >>>> + if (unlikely(!pmd_present(orig_pmd) || !pmd_trans_huge(orig_pmd))) >>>> + return false; >>>> + >>>> + page = pmd_page(orig_pmd); >>>> + if (unlikely(page_folio(page) != folio)) >>>> + return false; >>>> + >>>> + tlb_gather_mmu(&tlb, mm); >>>> + orig_pmd = pmdp_huge_get_and_clear(mm, addr, pmdp); >>>> + tlb_remove_pmd_tlb_entry(&tlb, pmdp, addr); >>>> + >>>> + /* >>>> + * Syncing against concurrent GUP-fast: >>>> + * - clear PMD; barrier; read refcount >>>> + * - inc refcount; barrier; read PMD >>>> + */ >>>> + smp_mb(); >>>> + >>>> + ref_count = folio_ref_count(folio); >>>> + map_count = folio_mapcount(folio); >>>> + >>>> + /* >>>> + * Order reads for folio refcount and dirty flag >>>> + * (see comments in __remove_mapping()). >>>> + */ >>>> + smp_rmb(); >>>> + >>>> + /* >>>> + * If the PMD or folio is redirtied at this point, or if there are >>>> + * unexpected references, we will give up to discard this folio >>>> + * and remap it. >>>> + * >>>> + * The only folio refs must be one from isolation plus the rmap(s). >>>> + */ >>>> + if (ref_count != map_count + 1 || folio_test_dirty(folio) || >>>> + pmd_dirty(orig_pmd)) { >>>> + set_pmd_at(mm, addr, pmdp, orig_pmd); >>>> + return false; >>>> + } >>>> + >>>> + folio_remove_rmap_pmd(folio, page, vma); >>>> + zap_deposited_table(mm, pmdp); >>>> + add_mm_counter(mm, MM_ANONPAGES, -HPAGE_PMD_NR); >>>> + folio_put(folio); >>> >>> IIUC, you missed handling mlock vma, see mlock_drain_local() in >>> try_to_unmap_one(). >> >> Good spot! >> >> I suddenly realized that I overlooked another thing: If we detect that a >> PMD-mapped THP is within the range of the VM_LOCKED VMA, we >> should check whether the TTU_IGNORE_MLOCK flag is set in >> try_to_unmap_one(). If the flag is set, we will remove the PMD mapping >> from the folio. Otherwise, the folio should be mlocked, which avoids >> splitting the folio and then mlocking each page again. > > My previous response above is flawed - sorry :( > > If we detect that a PMD-mapped THP is within the range of the > VM_LOCKED VMA. > > 1) If the TTU_IGNORE_MLOCK flag is set, we will try to remove the > PMD mapping from the folio, as this series has done. Right. > 2) If the flag is not set, the large folio should be mlocked to prevent it > from being picked during memory reclaim? Currently, we just leave it Yes. From commit 1acbc3f93614 ("mm: handle large folio when large folio in VM_LOCKED VMA range"), large folios of the mlocked VMA will be handled during page reclaim phase. > as is and do not to mlock it, IIUC. Original code already handle the mlock case after the PMD-mapped THP is split in try_to_unmap_one(): /* * If the folio is in an mlock()d vma, we must not swap it out. */ if (!(flags & TTU_IGNORE_MLOCK) && (vma->vm_flags & VM_LOCKED)) { /* Restore the mlock which got missed */ if (!folio_test_large(folio)) mlock_vma_folio(folio, vma); page_vma_mapped_walk_done(&pvmw); ret = false; break; }