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([2620:10d:c092:500::4:61b7]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a80f411bb3csm160072166b.116.2024.08.14.04.20.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Aug 2024 04:20:24 -0700 (PDT) Message-ID: <59725862-f4fc-456c-bafb-cbd302777881@gmail.com> Date: Wed, 14 Aug 2024 12:20:23 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/6] mm: Introduce a pageflag for partially mapped folios To: Barry Song Cc: akpm@linux-foundation.org, linux-mm@kvack.org, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, roman.gushchin@linux.dev, yuzhao@google.com, david@redhat.com, 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 References: <20240813120328.1275952-1-usamaarif642@gmail.com> <20240813120328.1275952-5-usamaarif642@gmail.com> Content-Language: en-US From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 14/08/2024 12:10, Barry Song wrote: > On Wed, Aug 14, 2024 at 12:03 AM 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 partially_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 = PG_active, >> PG_large_rmappable = 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 *page) >> 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 *page, 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 *folio) >> 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 = get_deferred_split_queue(folio); >> #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_DEFERRED); >> + if (partially_mapped) { >> + if (folio_test_pmd_mappable(folio)) >> + count_vm_event(THP_DEFERRED_SPLIT_PAGE); >> + count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFERRED); > > This code completely broke MTHP_STAT_SPLIT_DEFERRED for PMD_ORDER. It > added the folio to the deferred_list as entirely_mapped > (partially_mapped == false). > However, when partially_mapped becomes true, there's no opportunity to > add it again > as it has been there on the list. Are you consistently seeing the counter for > PMD_ORDER as 0? > Ah I see it, this should fix it? -void deferred_split_folio(struct folio *folio) +/* partially_mapped=false won't clear PG_partially_mapped folio flag */ +void deferred_split_folio(struct folio *folio, bool partially_mapped) { struct deferred_split *ds_queue = get_deferred_split_queue(folio); #ifdef CONFIG_MEMCG @@ -3485,14 +3488,14 @@ 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 (list_empty(&folio->_deferred_list)) { + if (partially_mapped) { + folio_set_partially_mapped(folio); if (folio_test_pmd_mappable(folio)) count_vm_event(THP_DEFERRED_SPLIT_PAGE); count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFERRED); + } + if (list_empty(&folio->_deferred_list)) { list_add_tail(&folio->_deferred_list, &ds_queue->split_queue); ds_queue->split_queue_len++; #ifdef CONFIG_MEMCG