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imf25.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf25.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1715078246; a=rsa-sha256; cv=none; b=IhZljibDq8W9ARGV6ieb+2MP6RJS0hUnxsO8tw69OY/9teqi0VtDn4NoAUzcNIgZFEdvLe 9sX0vYHZxHHlyzqMVcsanNsexn6I7HB6EwLskzIb9JYpyWrZ7/p6ABJo1FSa+ESE8BDoU3 4XPhY+2irGm/MSzgwO/VkFPo8svKrUc= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B6C981063; Tue, 7 May 2024 03:37:51 -0700 (PDT) Received: from [10.1.34.181] (unknown [10.1.34.181]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2A6423F587; Tue, 7 May 2024 03:37:24 -0700 (PDT) Message-ID: <13939ade-a99a-4075-8a26-9be7576b7e03@arm.com> Date: Tue, 7 May 2024 11:37:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/8] mm: memory: extend finish_fault() to support large folio Content-Language: en-GB To: Baolin Wang , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, david@redhat.com, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ying.huang@intel.com, 21cnbao@gmail.com, shy828301@gmail.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 7D9FDA0017 X-Stat-Signature: immmdixtnrybitxs98y4988upxucouzc X-HE-Tag: 1715078246-461184 X-HE-Meta: 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 ht06Azuc yJJysLN4c6sWyla2aZ6vJ4Eou+WhfIBxRsD9Ac35x5zv+pdKzAp31WZleUekdzS6QBVc9RrBdqvp7WLDoPqk08Q4Bpv4+lA4mEbDQyGF556sDQJQSSxQsnorDaV566OlVZLdm3Ub5cY7hB17PW31FFLaqDkwaKNZ6SaejGxb7q9J1N3Iuml5lfdRU1OCD4vzImn83rJgeM4pmzwwM8ggGcbTGqgx4IOaqDSdB 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 06/05/2024 09:46, Baolin Wang wrote: > Add large folio mapping establishment support for finish_fault() as a preparation, > to support multi-size THP allocation of anonymous shmem pages in the following > patches. > > Signed-off-by: Baolin Wang > --- > mm/memory.c | 43 +++++++++++++++++++++++++++++++++---------- > 1 file changed, 33 insertions(+), 10 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index eea6e4984eae..936377220b77 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4747,9 +4747,12 @@ vm_fault_t finish_fault(struct vm_fault *vmf) > { > struct vm_area_struct *vma = vmf->vma; > struct page *page; > + struct folio *folio; > vm_fault_t ret; > bool is_cow = (vmf->flags & FAULT_FLAG_WRITE) && > !(vma->vm_flags & VM_SHARED); > + int type, nr_pages, i; > + unsigned long addr = vmf->address; > > /* Did we COW the page? */ > if (is_cow) > @@ -4780,24 +4783,44 @@ vm_fault_t finish_fault(struct vm_fault *vmf) > return VM_FAULT_OOM; > } > > + folio = page_folio(page); > + nr_pages = folio_nr_pages(folio); > + > + if (unlikely(userfaultfd_armed(vma))) { > + nr_pages = 1; > + } else if (nr_pages > 1) { > + unsigned long start = ALIGN_DOWN(vmf->address, nr_pages * PAGE_SIZE); > + unsigned long end = start + nr_pages * PAGE_SIZE; > + > + /* In case the folio size in page cache beyond the VMA limits. */ > + addr = max(start, vma->vm_start); > + nr_pages = (min(end, vma->vm_end) - addr) >> PAGE_SHIFT; > + > + page = folio_page(folio, (addr - start) >> PAGE_SHIFT); I still don't really follow the logic in this else if block. Isn't it possible that finish_fault() gets called with a page from a folio that isn't aligned with vmf->address? For example, let's say we have a file who's size is 64K and which is cached in a single large folio in the page cache. But the file is mapped into a process at VA 16K to 80K. Let's say we fault on the first page (VA=16K). You will calculate start=0 and end=64K I think? Additionally, I think this path will end up mapping the entire folio (as long as it fits in the VMA). But this bypasses the fault-around configuration. As I think I mentioned against the RFC, this will inflate the RSS of the process and can cause behavioural changes as a result. I believe the current advice is to disable fault-around to prevent this kind of bloat when needed. It might be that you need a special variant of finish_fault() for shmem? > + } > vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, > - vmf->address, &vmf->ptl); > + addr, &vmf->ptl); > if (!vmf->pte) > return VM_FAULT_NOPAGE; > > /* Re-check under ptl */ > - if (likely(!vmf_pte_changed(vmf))) { > - struct folio *folio = page_folio(page); > - int type = is_cow ? MM_ANONPAGES : mm_counter_file(folio); > - > - set_pte_range(vmf, folio, page, 1, vmf->address); > - add_mm_counter(vma->vm_mm, type, 1); > - ret = 0; > - } else { > - update_mmu_tlb(vma, vmf->address, vmf->pte); > + if (nr_pages == 1 && unlikely(vmf_pte_changed(vmf))) { > + update_mmu_tlb(vma, addr, vmf->pte); > + ret = VM_FAULT_NOPAGE; > + goto unlock; > + } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) { > + for (i = 0; i < nr_pages; i++) > + update_mmu_tlb(vma, addr + PAGE_SIZE * i, vmf->pte + i); > ret = VM_FAULT_NOPAGE; > + goto unlock; > } > > + set_pte_range(vmf, folio, page, nr_pages, addr); > + type = is_cow ? MM_ANONPAGES : mm_counter_file(folio); > + add_mm_counter(vma->vm_mm, type, nr_pages); > + ret = 0; > + > +unlock: > pte_unmap_unlock(vmf->pte, vmf->ptl); > return ret; > }