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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> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=cZl3DKbU; spf=none (imf10.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: ittoe8w9z9nudkhmcarmpyyhus3nakoy X-Rspamd-Queue-Id: D66BB6001984 X-Rspamd-Server: rspam04 X-HE-Tag: 1630929706-9637 Content-Transfer-Encoding: quoted-printable 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: 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 pa= ge 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 chec= ks in >>>> __free_one_page() if PageReported is set. Or we will corrupt the fre= e list >>>> because list_add() will be called for pages already on another list. >>>> >>>> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging o= n isolated pageblock") >>>> Signed-off-by: Miaohe Lin >>>> --- >>>> =C2=A0 mm/page_isolation.c | 6 ++---- >>>> =C2=A0 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) >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 buddy_pfn =3D __find_buddy_pfn(pfn, order); >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 buddy =3D page + (buddy_pfn - pfn); >>>> =C2=A0 -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 if (!is_migrate_isolate_page(buddy)) { >>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 __isolate_free_page(page, order); >>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 isolated_page =3D true; >>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 = } >>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 = if (!is_migrate_isolate_page(buddy)) >>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 isolated_page =3D !!__isolate_free_page(page, order= ); >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>>> =20 >>> >>> Shouldn't we much rather force to ignore watermarks here and make sur= e __isolate_free_page() never fails? >> >> It seems it is not easy to force to ignore watermarks here. And it's n= ot a problem >> if __isolate_free_page() fails because we can do move_freepages_block(= ) anyway. >> What do you think? Many thanks. >=20 > I'm wondering if all this complexity in this function is even required.= What about something like this: (completely untested) >=20 > 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 *pag= e, int migratetype, int isol_ > =20 > static void unset_migratetype_isolate(struct page *page, unsigned mi= gratetype) > { > + bool buddy_merge_possible =3D false; > struct zone *zone; > unsigned long flags, nr_pages; > - bool isolated_page =3D false; > unsigned int order; > - unsigned long pfn, buddy_pfn; > - struct page *buddy; > =20 > zone =3D 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; > =20 > /* > - * Because freepage with more than pageblock_order on isolated > - * pageblock is restricted to merge due to freepage counting pr= oblem, > - * it is possible that there is free buddy page. > - * move_freepages_block() doesn't care of merge so we need othe= r > - * approach in order to merge them. Isolation and free will mak= e > - * these pages to be merged. > + * If our free page spans at least this whole pageblock and cou= ld > + * eventually get merged into an even bigger page, go via > + * __putback_isolated_page(), because move_freepages_block() wo= n't > + * trigger merging of free pages. > */ > if (PageBuddy(page)) { > order =3D buddy_order(page); > - if (order >=3D pageblock_order && order < MAX_ORDER - 1= ) { > - pfn =3D page_to_pfn(page); > - buddy_pfn =3D __find_buddy_pfn(pfn, order); > - buddy =3D page + (buddy_pfn - pfn); > - > - if (pfn_valid_within(buddy_pfn) && > - !is_migrate_isolate_page(buddy)) { > - __isolate_free_page(page, order); > - isolated_page =3D true; > - } > - } > + if (order >=3D pageblock_order && order < MAX_ORDER - 1= ) > + buddy_merge_possible =3D true; > } > =20 > /* > @@ -111,12 +98,12 @@ static void unset_migratetype_isolate(struct page = *page, unsigned migratetype) > * onlining - just onlined memory won't immediately be consid= ered for > * allocation. > */ > - if (!isolated_page) { > + if (!buddy_merge_possible) { > nr_pages =3D move_freepages_block(zone, page, migrate= type, 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=20 correctly said, it still is on the freelist ... So your fix is certainly correct :) --=20 Thanks, David / dhildenb