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[91.12.99.35]) by smtp.gmail.com with ESMTPSA id a10sm7117098wmj.44.2021.09.06.05.11.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Sep 2021 05:11:14 -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> <3b36529f-ab97-ddfe-0407-66f0cd1fd38d@redhat.com> Organization: Red Hat Message-ID: <2d06db75-5c26-8fe2-6883-ac99056a9894@redhat.com> Date: Mon, 6 Sep 2021 14:11:13 +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: <3b36529f-ab97-ddfe-0407-66f0cd1fd38d@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06.09.21 14:02, 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); >> } >> } >> >> > > Thanks! > > Reviewed-by: David Hildenbrand > To make the confusion perfect (sorry) :D I tripple-checked: In unset_migratetype_isolate() we check that is_migrate_isolate_page(page) holds, otherwise we return. We call __isolate_free_page() only for such pages. __isolate_free_page() won't perform watermark checks on is_migrate_isolate(). Consequently, __isolate_free_page() should never fail when called from unset_migratetype_isolate() If that's correct then we could instead maybe add a VM_BUG_ON() and a comment why this can't fail. Makes sense or am I missing something? -- Thanks, David / dhildenb