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[79.224.243.191]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a831051c49sm234050f8f.30.2025.06.26.06.16.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 26 Jun 2025 06:16:26 -0700 (PDT) Message-ID: <1a55f9f3-f5b1-4761-97ba-423756c707fe@redhat.com> Date: Thu, 26 Jun 2025 15:16:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/4] mm: Support batched unmap for lazyfree large folios during reclamation To: Lance Yang Cc: 21cnbao@gmail.com, akpm@linux-foundation.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, kasong@tencent.com, lance.yang@linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, ying.huang@intel.com, zhengtangquan@oppo.com References: <20250626092905.31305-1-ioworker0@gmail.com> <20250626124445.77865-1-ioworker0@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-Server: rspam03 X-Rspamd-Queue-Id: 5876E140013 X-Stat-Signature: ry3b66pc66rmm5dybmg11d6dxpyp4nwp X-Rspam-User: X-HE-Tag: 1750943790-921035 X-HE-Meta: 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 0VqBO9yQ GHn3M94MSI6pPQjBFAH4V96C4yyr42t2nihotdpKsner5W7pKL5ojsHBcnfpEW1wgxb6i9XNuZs6e7WUs19aMaTMXH0PhWpFk7SWLNV8pBCfSaHn95+k7KwU41XnCQLJZEce+XbUgqQtHJytQV6KjqvHph2y8MHNnCcke4q6i7vebmeyODQkCAWjV5T2XpPcoKn/9Ab68gflk8RWcTegYM9CXM6L6SBDSJdO0ISkDi6e0197vUhgye20cKKchFrjQTYuXLPWH17cIN/Ggr/w9/urECAUXJLNBw1++LNJRtLXZonh5YWTo2gDZiaha7LaDpSQ2PQSWZDQ5Gp3Y7FwQfQPZHS+sDnCG0QXdHo/22EUdc9mZInp4zWnVCYFTPyw7/M8yOSSzH2+Z9EYECITEXJqYAQfn2/FVdbp6Zs9buQ45TmD8Sy+x4J7Ucq+yR0sJTBeW1VvrchCPet0= 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 26.06.25 14:44, Lance Yang wrote: > > On 2025/6/26 17:29, Lance Yang wrote: >> Before I send out the real patch, I'd like to get some quick feedback to >> ensure I've understood the discussion correctly ;) >> >> Does this look like the right direction? >> >> diff --git a/mm/rmap.c b/mm/rmap.c >> index fb63d9256f09..5ebffe2137e4 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1845,23 +1845,37 @@ void folio_remove_rmap_pud(struct folio *folio, struct page *page, >> #endif >> } >> >> -/* We support batch unmapping of PTEs for lazyfree large folios */ >> -static inline bool can_batch_unmap_folio_ptes(unsigned long addr, >> - struct folio *folio, pte_t *ptep) >> +static inline unsigned int folio_unmap_pte_batch(struct folio *folio, >> + struct page_vma_mapped_walk *pvmw, >> + enum ttu_flags flags, pte_t pte) >> { >> const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; >> - int max_nr = folio_nr_pages(folio); >> - pte_t pte = ptep_get(ptep); >> + unsigned long end_addr, addr = pvmw->address; >> + struct vm_area_struct *vma = pvmw->vma; >> + unsigned int max_nr; >> + >> + if (flags & TTU_HWPOISON) >> + return 1; >> + if (!folio_test_large(folio)) >> + return 1; >> >> + /* We may only batch within a single VMA and a single page table. */ >> + end_addr = pmd_addr_end(addr, vma->vm_end); >> + max_nr = (end_addr - addr) >> PAGE_SHIFT; >> + >> + /* We only support lazyfree batching for now ... */ >> if (!folio_test_anon(folio) || folio_test_swapbacked(folio)) >> - return false; >> + return 1; >> if (pte_unused(pte)) >> - return false; >> - if (pte_pfn(pte) != folio_pfn(folio)) >> - return false; >> + return 1; >> + >> + /* ... where we must be able to batch the whole folio. */ >> + if (pte_pfn(pte) != folio_pfn(folio) || max_nr != folio_nr_pages(folio)) >> + return 1; >> + max_nr = folio_pte_batch(folio, addr, pvmw->pte, pte, max_nr, fpb_flags, >> + NULL, NULL, NULL); >> >> - return folio_pte_batch(folio, addr, ptep, pte, max_nr, fpb_flags, NULL, >> - NULL, NULL) == max_nr; >> + return (max_nr != folio_nr_pages(folio)) ? 1 : max_nr; >> } >> >> /* >> @@ -2024,9 +2038,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> if (pte_dirty(pteval)) >> folio_mark_dirty(folio); >> } else if (likely(pte_present(pteval))) { >> - if (folio_test_large(folio) && !(flags & TTU_HWPOISON) && >> - can_batch_unmap_folio_ptes(address, folio, pvmw.pte)) >> - nr_pages = folio_nr_pages(folio); >> + nr_pages = folio_unmap_pte_batch(folio, &pvmw, flags, pteval); >> end_addr = address + nr_pages * PAGE_SIZE; >> flush_cache_range(vma, address, end_addr); >> >> @@ -2206,13 +2218,16 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, >> hugetlb_remove_rmap(folio); >> } else { >> folio_remove_rmap_ptes(folio, subpage, nr_pages, vma); >> - folio_ref_sub(folio, nr_pages - 1); >> } >> if (vma->vm_flags & VM_LOCKED) >> mlock_drain_local(); >> - folio_put(folio); >> - /* We have already batched the entire folio */ >> - if (nr_pages > 1) >> + folio_put_refs(folio, nr_pages); >> + >> + /* >> + * If we are sure that we batched the entire folio and cleared >> + * all PTEs, we can just optimize and stop right here. >> + */ >> + if (nr_pages == folio_nr_pages(folio)) >> goto walk_done; >> continue; >> walk_abort: >> -- > > Oops ... Through testing on my machine, I found that the logic doesn't > behave as expected because I messed up the meaning of max_nr (the available > scan room in the page table) with folio_nr_pages(folio) :( > > With the following change: > > diff --git a/mm/rmap.c b/mm/rmap.c > index 5ebffe2137e4..b1407348e14e 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1850,9 +1850,9 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio, > enum ttu_flags flags, pte_t pte) > { > const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; > + unsigned int max_nr, nr_pages = folio_nr_pages(folio); > unsigned long end_addr, addr = pvmw->address; > struct vm_area_struct *vma = pvmw->vma; > - unsigned int max_nr; > > if (flags & TTU_HWPOISON) > return 1; > @@ -1870,12 +1870,13 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio, > return 1; > > /* ... where we must be able to batch the whole folio. */ Why is that still required? :) > - if (pte_pfn(pte) != folio_pfn(folio) || max_nr != folio_nr_pages(folio)) > + if (pte_pfn(pte) != folio_pfn(folio) || max_nr < nr_pages) > return 1; > - max_nr = folio_pte_batch(folio, addr, pvmw->pte, pte, max_nr, fpb_flags, > - NULL, NULL, NULL); > > - return (max_nr != folio_nr_pages(folio)) ? 1 : max_nr; > + max_nr = folio_pte_batch(folio, addr, pvmw->pte, pte, nr_pages, > + fpb_flags, NULL, NULL, NULL); > + > + return (max_nr != nr_pages) ? 1 : max_nr; Why is that still required? :) -- Cheers, David / dhildenb