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[91.12.99.35]) by smtp.gmail.com with ESMTPSA id l11sm7891776wrb.15.2021.09.06.04.50.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Sep 2021 04:50:10 -0700 (PDT) To: Miaohe Lin , akpm@linux-foundation.org Cc: vbabka@suse.cz, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210904091839.20270-1-linmiaohe@huawei.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page Message-ID: <5f7c4ac9-d17a-5af3-0326-1152cca38465@redhat.com> Date: Mon, 6 Sep 2021 13:50:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06.09.21 13:32, Miaohe Lin wrote: > On 2021/9/6 17:40, David Hildenbrand wrote: >> On 04.09.21 11:18, Miaohe Lin wrote: >>> If __isolate_free_page() failed, due to zone watermark check, the page is >>> still on the free list. But this page will be put back to free list again >>> via __putback_isolated_page() now. This may trigger page->flags checks in >>> __free_one_page() if PageReported is set. Or we will corrupt the free list >>> because list_add() will be called for pages already on another list. >>> >>> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock") >>> Signed-off-by: Miaohe Lin >>> --- >>>   mm/page_isolation.c | 6 ++---- >>>   1 file changed, 2 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c >>> index 9bb562d5d194..7d70d772525c 100644 >>> --- a/mm/page_isolation.c >>> +++ b/mm/page_isolation.c >>> @@ -93,10 +93,8 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) >>>               buddy_pfn = __find_buddy_pfn(pfn, order); >>>               buddy = page + (buddy_pfn - pfn); >>>   -            if (!is_migrate_isolate_page(buddy)) { >>> -                __isolate_free_page(page, order); >>> -                isolated_page = true; >>> -            } >>> +            if (!is_migrate_isolate_page(buddy)) >>> +                isolated_page = !!__isolate_free_page(page, order); >>>           } >>>       } >>> >> >> Shouldn't we much rather force to ignore watermarks here and make sure __isolate_free_page() never fails? > > It seems it is not easy to force to ignore watermarks here. And it's not a problem > if __isolate_free_page() fails because we can do move_freepages_block() anyway. > What do you think? Many thanks. I'm wondering if all this complexity in this function is even required. What about something like this: (completely untested) diff --git a/mm/page_isolation.c b/mm/page_isolation.c index bddf788f45bf..29ff2fcb339c 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -66,12 +66,10 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) { + bool buddy_merge_possible = false; struct zone *zone; unsigned long flags, nr_pages; - bool isolated_page = false; unsigned int order; - unsigned long pfn, buddy_pfn; - struct page *buddy; zone = page_zone(page); spin_lock_irqsave(&zone->lock, flags); @@ -79,26 +77,15 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) goto out; /* - * Because freepage with more than pageblock_order on isolated - * pageblock is restricted to merge due to freepage counting problem, - * it is possible that there is free buddy page. - * move_freepages_block() doesn't care of merge so we need other - * approach in order to merge them. Isolation and free will make - * these pages to be merged. + * If our free page spans at least this whole pageblock and could + * eventually get merged into an even bigger page, go via + * __putback_isolated_page(), because move_freepages_block() won't + * trigger merging of free pages. */ if (PageBuddy(page)) { order = buddy_order(page); - if (order >= pageblock_order && order < MAX_ORDER - 1) { - pfn = page_to_pfn(page); - buddy_pfn = __find_buddy_pfn(pfn, order); - buddy = page + (buddy_pfn - pfn); - - if (pfn_valid_within(buddy_pfn) && - !is_migrate_isolate_page(buddy)) { - __isolate_free_page(page, order); - isolated_page = true; - } - } + if (order >= pageblock_order && order < MAX_ORDER - 1) + buddy_merge_possible = true; } /* @@ -111,12 +98,12 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype) * onlining - just onlined memory won't immediately be considered for * allocation. */ - if (!isolated_page) { + if (!buddy_merge_possible) { nr_pages = move_freepages_block(zone, page, migratetype, NULL); __mod_zone_freepage_state(zone, nr_pages, migratetype); } set_pageblock_migratetype(page, migratetype); - if (isolated_page) + if (buddy_merge_possible) __putback_isolated_page(page, order, migratetype); zone->nr_isolate_pageblock--; out: -- Thanks, David / dhildenb