From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-98.freemail.mail.aliyun.com (out30-98.freemail.mail.aliyun.com [115.124.30.98]) (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 7CF7F230275 for ; Tue, 14 Jan 2025 03:40:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.98 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736826018; cv=none; b=QqSyvy1TSOdrQe0YzRYdivjD4FUnxjYKIZaB7sn4FjmnysilJPVeaa2rc4+gBiLkwegDFObUgXvEWAtVQAULM9s1LqdZw/yXV6BfI4fZ9jlvVY6fpP5vvJZ0EiTuzcBZPY+z1yqJO/vD81jHg4XZp0TC2ShgC3saNsHoxffj1OU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736826018; c=relaxed/simple; bh=E8OCWQ03y0uAZcyWv6gjKrtjS4sndKH2v/stzv1hyL0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=u845fYlERfGzWJVe2MXlMNkRBwOap4wlF7dVb6HtlBphtnwIvPNVdSJZ7QCkhp42CjoFHaVVb/pr6gr056ELbkfZnIss/SOaLAzTgc7IhFbJttMu/zf0PeHWn+dLZ6dGbhOqtVhm37+DAhj8SKBv7ksg9JIL8s2Sqt1g1rfxUTk= 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=PgjjNH7N; arc=none smtp.client-ip=115.124.30.98 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="PgjjNH7N" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1736826007; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=ED3v0KZ62Otclzj/DtPlHw7G1s3gURYmmZedtowKKdY=; b=PgjjNH7N4PYC1crtK1RlhVquOiTALTD1eq0v0QqLL+XyNH+6y04YBdXCziYWi5XsWwNN7kSDJGYy7WRngsm9miPR94QlUApChV+RanBUPn2e8BHAK2uKmBT8a/mqGuSd1ch0uOeR6aYKHiEGO6/fQbgywQe/GrKJMqkZHxbJd9Q= Received: from 30.74.144.113(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WNdJbji_1736826004 cluster:ay36) by smtp.aliyun-inc.com; Tue, 14 Jan 2025 11:40:05 +0800 Message-ID: Date: Tue, 14 Jan 2025 11:40:04 +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 v2 4/4] mm: Avoid splitting pmd for lazyfree pmd-mapped THP in try_to_unmap To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org Cc: chrisl@kernel.org, david@redhat.com, ioworker0@gmail.com, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, linux-riscv@lists.infradead.org, ying.huang@intel.com, zhengtangquan@oppo.com, lorenzo.stoakes@oracle.com References: <20250113033901.68951-1-21cnbao@gmail.com> <20250113033901.68951-5-21cnbao@gmail.com> From: Baolin Wang In-Reply-To: <20250113033901.68951-5-21cnbao@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2025/1/13 11:39, Barry Song wrote: > From: Barry Song > > The try_to_unmap_one() function currently handles PMD-mapped THPs > inefficiently. It first splits the PMD into PTEs, copies the dirty > state from the PMD to the PTEs, iterates over the PTEs to locate > the dirty state, and then marks the THP as swap-backed. This process > involves unnecessary PMD splitting and redundant iteration. Instead, > this functionality can be efficiently managed in > __discard_anon_folio_pmd_locked(), avoiding the extra steps and > improving performance. > > The following microbenchmark redirties folios after invoking MADV_FREE, > then measures the time taken to perform memory reclamation (actually > set those folios swapbacked again) on the redirtied folios. > > #include > #include > #include > #include > > #define SIZE 128*1024*1024 // 128 MB > > int main(int argc, char *argv[]) > { > while(1) { > volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > > memset((void *)p, 1, SIZE); > madvise((void *)p, SIZE, MADV_FREE); > /* redirty after MADV_FREE */ > memset((void *)p, 1, SIZE); > > clock_t start_time = clock(); > madvise((void *)p, SIZE, MADV_PAGEOUT); > clock_t end_time = clock(); > > double elapsed_time = (double)(end_time - start_time) / CLOCKS_PER_SEC; > printf("Time taken by reclamation: %f seconds\n", elapsed_time); > > munmap((void *)p, SIZE); > } > return 0; > } > > Testing results are as below, > w/o patch: > ~ # ./a.out > Time taken by reclamation: 0.007300 seconds > Time taken by reclamation: 0.007226 seconds > Time taken by reclamation: 0.007295 seconds > Time taken by reclamation: 0.007731 seconds > Time taken by reclamation: 0.007134 seconds > Time taken by reclamation: 0.007285 seconds > Time taken by reclamation: 0.007720 seconds > Time taken by reclamation: 0.007128 seconds > Time taken by reclamation: 0.007710 seconds > Time taken by reclamation: 0.007712 seconds > Time taken by reclamation: 0.007236 seconds > Time taken by reclamation: 0.007690 seconds > Time taken by reclamation: 0.007174 seconds > Time taken by reclamation: 0.007670 seconds > Time taken by reclamation: 0.007169 seconds > Time taken by reclamation: 0.007305 seconds > Time taken by reclamation: 0.007432 seconds > Time taken by reclamation: 0.007158 seconds > Time taken by reclamation: 0.007133 seconds > … > > w/ patch > > ~ # ./a.out > Time taken by reclamation: 0.002124 seconds > Time taken by reclamation: 0.002116 seconds > Time taken by reclamation: 0.002150 seconds > Time taken by reclamation: 0.002261 seconds > Time taken by reclamation: 0.002137 seconds > Time taken by reclamation: 0.002173 seconds > Time taken by reclamation: 0.002063 seconds > Time taken by reclamation: 0.002088 seconds > Time taken by reclamation: 0.002169 seconds > Time taken by reclamation: 0.002124 seconds > Time taken by reclamation: 0.002111 seconds > Time taken by reclamation: 0.002224 seconds > Time taken by reclamation: 0.002297 seconds > Time taken by reclamation: 0.002260 seconds > Time taken by reclamation: 0.002246 seconds > Time taken by reclamation: 0.002272 seconds > Time taken by reclamation: 0.002277 seconds > Time taken by reclamation: 0.002462 seconds > … > > This patch significantly speeds up try_to_unmap_one() by allowing it > to skip redirtied THPs without splitting the PMD. > > Suggested-by: Baolin Wang > Suggested-by: Lance Yang > Signed-off-by: Barry Song > --- > mm/huge_memory.c | 17 ++++++++++++++--- > mm/rmap.c | 11 ++++++++++- > 2 files changed, 24 insertions(+), 4 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 3d3ebdc002d5..aea49f7125f1 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3070,8 +3070,12 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > int ref_count, map_count; > pmd_t orig_pmd = *pmdp; > > - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd)) > + if (pmd_dirty(orig_pmd)) > + folio_set_dirty(folio); > + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > + folio_set_swapbacked(folio); > return false; > + } > > orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp); > > @@ -3098,8 +3102,15 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, > * > * The only folio refs must be one from isolation plus the rmap(s). > */ > - if (folio_test_dirty(folio) || pmd_dirty(orig_pmd) || > - ref_count != map_count + 1) { > + if (pmd_dirty(orig_pmd)) > + folio_set_dirty(folio); > + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > + folio_set_swapbacked(folio); > + set_pmd_at(mm, addr, pmdp, orig_pmd); > + return false; > + } > + > + if (ref_count != map_count + 1) { > set_pmd_at(mm, addr, pmdp, orig_pmd); > return false; > } > diff --git a/mm/rmap.c b/mm/rmap.c > index 3ef659310797..02c4e4b2cd7b 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1671,7 +1671,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); > pte_t pteval; > struct page *subpage; > - bool anon_exclusive, ret = true; > + bool anon_exclusive, lazyfree, ret = true; > struct mmu_notifier_range range; > enum ttu_flags flags = (enum ttu_flags)(long)arg; > int nr_pages = 1; > @@ -1724,9 +1724,18 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > } > > if (!pvmw.pte) { > + lazyfree = folio_test_anon(folio) && !folio_test_swapbacked(folio); You've checked lazyfree here, so can we remove the duplicate check in unmap_huge_pmd_locked()? Then the code should be: if (lazyfree && unmap_huge_pmd_locked(...)) goto walk_done; > if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, > folio)) > goto walk_done; > + /* > + * unmap_huge_pmd_locked has either already marked > + * the folio as swap-backed or decided to retain it > + * due to GUP or speculative references. > + */ > + if (lazyfree) > + goto walk_abort; > > if (flags & TTU_SPLIT_HUGE_PMD) { > /*