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[2003:cb:c74b:bf00:182c:d606:87cf:6fea]) by smtp.gmail.com with ESMTPSA id h12-20020a05600c314c00b0041be9cb540esm15770955wmo.18.2024.05.06.05.05.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 May 2024 05:05:48 -0700 (PDT) Message-ID: <0226a6f7-26ac-48b0-932d-1b7201cde1d7@redhat.com> Date: Mon, 6 May 2024 14:05:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 6/6] mm: swap: entirely map large folios found in swapcache To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org Cc: baolin.wang@linux.alibaba.com, chrisl@kernel.org, hanchuanhua@oppo.com, hannes@cmpxchg.org, hughd@google.com, kasong@tencent.com, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, xiang@kernel.org, ying.huang@intel.com, yosryahmed@google.com, yuzhao@google.com, ziy@nvidia.com References: <20240503005023.174597-1-21cnbao@gmail.com> <20240503005023.174597-7-21cnbao@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 156C840027 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 5hhdyfiq6yhwbeqyo697ipoqspiu5q4b X-HE-Tag: 1714997152-473685 X-HE-Meta: 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 F9Fwu7Fu JgYBrwtuUbTnsrXI0Dm6K6BfYja38RlceNT4XNxnJWNjT+oS8PbsGnz1a5f1JgCUzoWkt+ApCCgjMGpEjkBl2zyispTaKuS83fVjFPwI1K36UsN2pelXDnruTRVg3VNszlv0+mTmhzg1qWclNNbeMVxuT+QKYEzdqFOlago4+vX4dFwrzvzqLvo2fJ4ZcFipe/k1MGOp9k3HeRiGLC4UNYtt604GofC4xvMf7Zt3111Ls9GNCblK4YI5xYq/UV6ZCJoOYRJ5PirRKF1Iyrs7vaUCqjczfvVz7knC5nYIlg32UsWiDTI9LlxQykvDhECgssKhGXkPjgvTuYZ9DfJTjeYsOdGCofiqYnoHRZITlS10iKbebDzLB5Mcn9PRM2Wf2pGrQ4WcJ/D/VBJOlVQv1yoE6HulSxiklt4PwHbFwT/jPv00audnbv0mI41h1cDqLSpkGtobiHAXqstunPP62UbJQog== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 03.05.24 02:50, Barry Song wrote: > From: Chuanhua Han > > When a large folio is found in the swapcache, the current implementation > requires calling do_swap_page() nr_pages times, resulting in nr_pages > page faults. This patch opts to map the entire large folio at once to > minimize page faults. Additionally, redundant checks and early exits > for ARM64 MTE restoring are removed. > > Signed-off-by: Chuanhua Han > Co-developed-by: Barry Song > Signed-off-by: Barry Song > --- > mm/memory.c | 60 ++++++++++++++++++++++++++++++++++++++++++----------- > 1 file changed, 48 insertions(+), 12 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 22e7c33cc747..940fdbe69fa1 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3968,6 +3968,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > pte_t pte; > vm_fault_t ret = 0; > void *shadow = NULL; > + int nr_pages = 1; > + unsigned long page_idx = 0; > + unsigned long address = vmf->address; > + pte_t *ptep; > > if (!pte_unmap_same(vmf)) > goto out; > @@ -4166,6 +4170,36 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > goto out_nomap; > } > > + ptep = vmf->pte; > + if (folio_test_large(folio) && folio_test_swapcache(folio)) { > + int nr = folio_nr_pages(folio); > + unsigned long idx = folio_page_idx(folio, page); > + unsigned long folio_start = vmf->address - idx * PAGE_SIZE; > + unsigned long folio_end = folio_start + nr * PAGE_SIZE; > + pte_t *folio_ptep; > + pte_t folio_pte; > + > + if (unlikely(folio_start < max(vmf->address & PMD_MASK, vma->vm_start))) > + goto check_folio; > + if (unlikely(folio_end > pmd_addr_end(vmf->address, vma->vm_end))) > + goto check_folio; > + > + folio_ptep = vmf->pte - idx; > + folio_pte = ptep_get(folio_ptep); > + if (!pte_same(folio_pte, pte_move_swp_offset(vmf->orig_pte, -idx)) || > + swap_pte_batch(folio_ptep, nr, folio_pte) != nr) > + goto check_folio; > + > + page_idx = idx; > + address = folio_start; > + ptep = folio_ptep; > + nr_pages = nr; > + entry = folio->swap; > + page = &folio->page; > + } > + > +check_folio: > + > /* > * PG_anon_exclusive reuses PG_mappedtodisk for anon pages. A swap pte > * must never point at an anonymous page in the swapcache that is > @@ -4225,12 +4259,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > * We're already holding a reference on the page but haven't mapped it > * yet. > */ > - swap_free_nr(entry, 1); > + swap_free_nr(entry, nr_pages); > if (should_try_to_free_swap(folio, vma, vmf->flags)) > folio_free_swap(folio); > > - inc_mm_counter(vma->vm_mm, MM_ANONPAGES); > - dec_mm_counter(vma->vm_mm, MM_SWAPENTS); > + folio_ref_add(folio, nr_pages - 1); > + add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages); > + add_mm_counter(vma->vm_mm, MM_SWAPENTS, -nr_pages); > pte = mk_pte(page, vma->vm_page_prot); > > /* > @@ -4240,34 +4275,35 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > * exclusivity. > */ > if (!folio_test_ksm(folio) && > - (exclusive || folio_ref_count(folio) == 1)) { > + (exclusive || (folio_ref_count(folio) == nr_pages && > + folio_nr_pages(folio) == nr_pages))) { > if (vmf->flags & FAULT_FLAG_WRITE) { > pte = maybe_mkwrite(pte_mkdirty(pte), vma); > vmf->flags &= ~FAULT_FLAG_WRITE; I fail to convince myself that this change is correct, and if it is correct, it's confusing (I think there is a dependency on folio_free_swap() having been called and succeeding, such that we don't have a folio that is in the swapcache at this point). Why can't we move the folio_ref_add() after this check and just leave the check as it is? "folio_ref_count(folio) == 1" is as clear as it gets: we hold the single reference, so we can do with this thing whatever we want: it's certainly exclusive. No swapcache, no other people mapping it. -- Cheers, David / dhildenb