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Tue, 30 Apr 2024 01:35:02 -0700 (PDT) MIME-Version: 1.0 References: <20240429132308.38794-1-ioworker0@gmail.com> <20240429132308.38794-4-ioworker0@gmail.com> In-Reply-To: <20240429132308.38794-4-ioworker0@gmail.com> From: Barry Song <21cnbao@gmail.com> Date: Tue, 30 Apr 2024 20:34:51 +1200 Message-ID: Subject: Re: [PATCH v3 3/3] mm/vmscan: avoid split lazyfree THP during shrink_folio_list() To: Lance Yang Cc: akpm@linux-foundation.org, willy@infradead.org, maskray@google.com, ziy@nvidia.com, ryan.roberts@arm.com, david@redhat.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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 5i9na6bya9esu4n7exmb4546uz9reafi X-Rspam-User: X-Rspamd-Queue-Id: 5370C10000B X-Rspamd-Server: rspam05 X-HE-Tag: 1714466103-545018 X-HE-Meta: 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 JLOxLs4I Joc3Nky5MV3ij8X/bLLwAZt64XeaWQVH15ztwpKBjQ64UBxJyPyA4JZbDxATnJVoZFLM78uvvrHx5clazcLkuQcrJ54usbfJyq7uN0D/todsFHPxDetYcKhF2SzGZ5/9cyV92Ct6qBYVF2t+f0pdQyCl0WXuDsJdy8h9yPMDKs9kr4S69MoBWEXMfTTuQfFw4RZDFCjC8xMRa4lKxfXSlK/S/xCORUJZE5UvgTjrc3UznesP0pVzd38w0bnK8lI/92mYlUj2Bi3hS4jEdoYvpDJBFTpq2Bb65KRE6nabve6JXA7syYkI+rD2BVHoH7GcYYjeO9skEFG2kp9qubCYmh14b9TpFksxzszkfcRViX7NDg1MoUrqFZN9aM7ou+zx5ea179aKUeDmvUkrZymv2YVo6+tn3cINiPkRQw+AtTKC3Y3vKujxmyjY9aQ== 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 Tue, Apr 30, 2024 at 1:23=E2=80=AFAM Lance Yang wr= ote: > > 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 | 2 ++ > mm/huge_memory.c | 75 +++++++++++++++++++++++++++++++++++++++++ > mm/rmap.c | 3 ++ > 3 files changed, 80 insertions(+) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 2daadfcc6776..fd330f72b4f3 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -38,6 +38,8 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_a= rea_struct *vma, > unsigned long cp_flags); > void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long add= ress, > pmd_t *pmd, bool freeze, struct folio *folio); > +bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long add= r, > + pmd_t *pmdp, struct folio *folio); > > vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool writ= e); > vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool writ= e); > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 145505a1dd05..d35d526ed48f 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2690,6 +2690,81 @@ 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 =3D vma->vm_mm; > + int ref_count, map_count; > + pmd_t orig_pmd =3D *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 =3D pmd_page(orig_pmd); > + if (unlikely(page_folio(page) !=3D folio)) > + return false; > + > + tlb_gather_mmu(&tlb, mm); > + orig_pmd =3D 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 =3D folio_ref_count(folio); > + map_count =3D 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 ar= e > + * 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 !=3D 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); > + > + return true; > +} > + > +bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long add= r, > + 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)); > + > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > + if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) > + return __discard_trans_pmd_locked(vma, addr, pmdp, folio)= ; > +#endif this is weird and huge_memory.c is only built with CONFIG_TRANSPARENT_HUGEPAGE =3D y; mm/Makefile: obj-$(CONFIG_TRANSPARENT_HUGEPAGE) +=3D huge_memory.o khugepaged.o > + > + return false; > +} > + > static void remap_page(struct folio *folio, unsigned long nr) > { > int i =3D 0; > diff --git a/mm/rmap.c b/mm/rmap.c > index e42f436c7ff3..ab37af4f47aa 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1677,6 +1677,9 @@ static bool try_to_unmap_one(struct folio *folio, s= truct 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; this is making mm/rmap.c:1680: undefined reference to `unmap_huge_pmd_locked' mm/rmap.c:1687: undefined reference to `split_huge_pmd_locked' > /* > * We temporarily have to drop the PTL and start = once > * again from that now-PTE-mapped page table. > -- > 2.33.1 >