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[91.12.99.35]) by smtp.gmail.com with ESMTPSA id l26sm7054854wmi.13.2021.09.06.05.01.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Sep 2021 05:01:43 -0700 (PDT) Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page From: David Hildenbrand 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> <5f7c4ac9-d17a-5af3-0326-1152cca38465@redhat.com> Organization: Red Hat Message-ID: <2b103abc-2921-9d8a-7280-1d6b451c34f4@redhat.com> Date: Mon, 6 Sep 2021 14:01:42 +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: <5f7c4ac9-d17a-5af3-0326-1152cca38465@redhat.com> 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 13:50, David Hildenbrand wrote: > 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: Okay, I just had another look -- that won't work because as you correctly said, it still is on the freelist ... So your fix is certainly correct :) -- Thanks, David / dhildenb