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Received: from 30.97.56.67(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W6-h3d7_1715054460) by smtp.aliyun-inc.com; Tue, 07 May 2024 12:01:01 +0800 Message-ID: Date: Tue, 7 May 2024 12:00:59 +0800 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 , akpm@linux-foundation.org Cc: 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: <20240501042700.83974-4-ioworker0@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 9DFA41C0003 X-Stat-Signature: hnuw3p5ur1fx6u6ms9no66p3nrbkyje3 X-Rspam-User: X-HE-Tag: 1715054466-41602 X-HE-Meta: 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 T71LP0LQ V5W97hrvyHz1Qp6a8EJNks+OavICgydb/fgF8D6rrLEjPjwbRRTfK42+drArFb4gs81b7FRekxVmexwrtBifdc1pC3Yf4fypmkFlvbBQTQGv8CqynXhBHhzEeZ6UNELKv9AaDhqcDeK3v3edb7eEnH9JY82MdvCIdHC9hoSB9Sg7tiEs4Q5rkDTvUCLl/TirBnRkkiejZ/uPLObJpZ0YbN0ySlp1X8SYE+IERdoVP3qMFUQy7wB9KU+ejS+Bz/U3ZD+H8qribewAp9mYJcokd11Tj2/UsDpzjHMGUNhsxm1fiw0mYpCRT0nJxDkOxf4BKhzp3Hb1F4KFmhCjwEKr9hmpsTBwdRU9IcMa/sBIg2rLxp1+uZpJCxkFivl+QJQBFAIqQtI+d1aHACTVDTo4QnAN1i3/sSxHcKo2B 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 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(). > + > + return true; > +} > + > +bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, > + pmd_t *pmdp, struct folio *folio) > +{ > + VM_WARN_ON_FOLIO(!folio_test_pmd_mappable(folio), folio); > + VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); > + VM_WARN_ON_ONCE(!IS_ALIGNED(addr, HPAGE_PMD_SIZE)); > + > + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) > + return __discard_trans_pmd_locked(vma, addr, pmdp, folio); Why add a new function, which is only used by unmap_huge_pmd_locked()? Seems can be folded in unmap_huge_pmd_locked(), but not a strong preference:) > + > + return false; > +} > + > static void remap_page(struct folio *folio, unsigned long nr) > { > int i = 0; > diff --git a/mm/rmap.c b/mm/rmap.c > index 432601154583..1d3d30cb752c 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1675,6 +1675,9 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > } > > if (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD)) { > + if (unmap_huge_pmd_locked(vma, range.start, pvmw.pmd, > + folio)) > + goto walk_done; > /* > * We temporarily have to drop the PTL and start once > * again from that now-PTE-mapped page table.