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Tue, 13 Aug 2024 20:31:09 -0700 (PDT) MIME-Version: 1.0 References: <20240813120328.1275952-1-usamaarif642@gmail.com> <20240813120328.1275952-5-usamaarif642@gmail.com> In-Reply-To: <20240813120328.1275952-5-usamaarif642@gmail.com> From: Yu Zhao Date: Tue, 13 Aug 2024 21:30:31 -0600 Message-ID: Subject: Re: [PATCH v3 4/6] mm: Introduce a pageflag for partially mapped folios To: Usama Arif Cc: akpm@linux-foundation.org, linux-mm@kvack.org, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, roman.gushchin@linux.dev, david@redhat.com, baohua@kernel.org, ryan.roberts@arm.com, rppt@kernel.org, willy@infradead.org, cerasuolodomenico@gmail.com, corbet@lwn.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: f1imu9dy6oowcjfdes7or5qheccjthf5 X-Rspamd-Queue-Id: 080C718001D X-Rspamd-Server: rspam11 X-HE-Tag: 1723606270-104630 X-HE-Meta: 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 YbDXzx52 zxkFmw1FxNHo5z53uuf1wgV7OQaffkCSp04C23tIwB6JdkUzj/fmMppwxCSgEnYkAQYbyy4RiSQzVGiqYCdC9+wsD2sA+y4qJg2QGwk9s5tUigjgOg5VDpSGvPqZJWS7l+Z60i16iYcJHgHVI0sIdxiVZUx/QpqfSQTY67jK53+NVVz9+1ZWEvfQbfSQW2epuwgLG 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, Aug 13, 2024 at 6:03=E2=80=AFAM Usama Arif = wrote: > > Currently folio->_deferred_list is used to keep track of > partially_mapped folios that are going to be split under memory > pressure. In the next patch, all THPs that are faulted in and collapsed > by khugepaged are also going to be tracked using _deferred_list. > > This patch introduces a pageflag to be able to distinguish between > partially mapped folios and others in the deferred_list at split time in > deferred_split_scan. Its needed as __folio_remove_rmap decrements > _mapcount, _large_mapcount and _entire_mapcount, hence it won't be > possible to distinguish between partially mapped folios and others in > deferred_split_scan. > > Eventhough it introduces an extra flag to track if the folio is > partially mapped, there is no functional change intended with this > patch and the flag is not useful in this patch itself, it will > become useful in the next patch when _deferred_list has non partially > mapped folios. > > Signed-off-by: Usama Arif > --- > include/linux/huge_mm.h | 4 ++-- > include/linux/page-flags.h | 3 +++ > mm/huge_memory.c | 21 +++++++++++++-------- > mm/hugetlb.c | 1 + > mm/internal.h | 4 +++- > mm/memcontrol.c | 3 ++- > mm/migrate.c | 3 ++- > mm/page_alloc.c | 5 +++-- > mm/rmap.c | 3 ++- > mm/vmscan.c | 3 ++- > 10 files changed, 33 insertions(+), 17 deletions(-) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 4c32058cacfe..969f11f360d2 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -321,7 +321,7 @@ static inline int split_huge_page(struct page *page) > { > return split_huge_page_to_list_to_order(page, NULL, 0); > } > -void deferred_split_folio(struct folio *folio); > +void deferred_split_folio(struct folio *folio, bool partially_mapped); > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > unsigned long address, bool freeze, struct folio *folio); > @@ -495,7 +495,7 @@ static inline int split_huge_page(struct page *page) > { > return 0; > } > -static inline void deferred_split_folio(struct folio *folio) {} > +static inline void deferred_split_folio(struct folio *folio, bool partia= lly_mapped) {} > #define split_huge_pmd(__vma, __pmd, __address) \ > do { } while (0) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index a0a29bd092f8..cecc1bad7910 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -182,6 +182,7 @@ enum pageflags { > /* At least one page in this folio has the hwpoison flag set */ > PG_has_hwpoisoned =3D PG_active, > PG_large_rmappable =3D PG_workingset, /* anon or file-backed */ > + PG_partially_mapped, /* was identified to be partially mapped */ > }; > > #define PAGEFLAGS_MASK ((1UL << NR_PAGEFLAGS) - 1) > @@ -861,8 +862,10 @@ static inline void ClearPageCompound(struct page *pa= ge) > ClearPageHead(page); > } > FOLIO_FLAG(large_rmappable, FOLIO_SECOND_PAGE) > +FOLIO_FLAG(partially_mapped, FOLIO_SECOND_PAGE) > #else > FOLIO_FLAG_FALSE(large_rmappable) > +FOLIO_FLAG_FALSE(partially_mapped) > #endif > > #define PG_head_mask ((1UL << PG_head)) > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 6df0e9f4f56c..c024ab0f745c 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3397,6 +3397,7 @@ int split_huge_page_to_list_to_order(struct page *p= age, struct list_head *list, > * page_deferred_list. > */ > list_del_init(&folio->_deferred_list); > + folio_clear_partially_mapped(folio); > } > spin_unlock(&ds_queue->split_queue_lock); > if (mapping) { > @@ -3453,11 +3454,12 @@ void __folio_undo_large_rmappable(struct folio *f= olio) > if (!list_empty(&folio->_deferred_list)) { > ds_queue->split_queue_len--; > list_del_init(&folio->_deferred_list); > + folio_clear_partially_mapped(folio); > } > spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags); > } > > -void deferred_split_folio(struct folio *folio) > +void deferred_split_folio(struct folio *folio, bool partially_mapped) > { > struct deferred_split *ds_queue =3D get_deferred_split_queue(foli= o); > #ifdef CONFIG_MEMCG > @@ -3485,14 +3487,17 @@ void deferred_split_folio(struct folio *folio) > if (folio_test_swapcache(folio)) > return; > > - if (!list_empty(&folio->_deferred_list)) > - return; > - > spin_lock_irqsave(&ds_queue->split_queue_lock, flags); > + if (partially_mapped) > + folio_set_partially_mapped(folio); > + else > + folio_clear_partially_mapped(folio); > if (list_empty(&folio->_deferred_list)) { > - if (folio_test_pmd_mappable(folio)) > - count_vm_event(THP_DEFERRED_SPLIT_PAGE); > - count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFER= RED); > + if (partially_mapped) { > + if (folio_test_pmd_mappable(folio)) > + count_vm_event(THP_DEFERRED_SPLIT_PAGE); > + count_mthp_stat(folio_order(folio), MTHP_STAT_SPL= IT_DEFERRED); > + } > list_add_tail(&folio->_deferred_list, &ds_queue->split_qu= eue); > ds_queue->split_queue_len++; > #ifdef CONFIG_MEMCG > @@ -3541,6 +3546,7 @@ static unsigned long deferred_split_scan(struct shr= inker *shrink, > } else { > /* We lost race with folio_put() */ > list_del_init(&folio->_deferred_list); > + folio_clear_partially_mapped(folio); > ds_queue->split_queue_len--; > } > if (!--sc->nr_to_scan) > @@ -3558,7 +3564,6 @@ static unsigned long deferred_split_scan(struct shr= inker *shrink, > next: > folio_put(folio); > } > - Unintentional change above? > spin_lock_irqsave(&ds_queue->split_queue_lock, flags); > list_splice_tail(&list, &ds_queue->split_queue); > spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags); > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 1fdd9eab240c..2ae2d9a18e40 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1758,6 +1758,7 @@ static void __update_and_free_hugetlb_folio(struct = hstate *h, > free_gigantic_folio(folio, huge_page_order(h)); > } else { > INIT_LIST_HEAD(&folio->_deferred_list); > + folio_clear_partially_mapped(folio); Why does it need to clear a flag that should never be set on hugeTLB folios= ? HugeTLB does really use _deferred_list -- it clears it only to avoid bad_page() because of the overlapping fields: void *_hugetlb_subpool; void *_hugetlb_cgroup;