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[2003:cb:c705:2200:178b:7244:2a1f:b5d8]) by smtp.gmail.com with ESMTPSA id bg20-20020a05600c3c9400b0037fa5c422c8sm5141804wmb.48.2022.03.30.06.16.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Mar 2022 06:16:18 -0700 (PDT) Message-ID: Date: Wed, 30 Mar 2022 15:16:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH v2 2/2] mm: fix contiguous memmap assumptions about alloc/free pages To: Chen Wandun , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, willy@infradead.org References: <20220330102534.1053240-1-chenwandun@huawei.com> <20220330102534.1053240-3-chenwandun@huawei.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220330102534.1053240-3-chenwandun@huawei.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=JjRdnaMA; spf=none (imf07.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: shxubmugdzr453x69tfyjjwhmpk3y7gg X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: AB4494000B X-HE-Tag: 1648646183-647074 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 30.03.22 12:25, Chen Wandun wrote: > It isn't true for only SPARSEMEM configs to assume that a compound page > has virtually contiguous page structs, so use nth_page to iterate each > page. I really don't see how that is currently the case. The buddy deals with order < MAX_ORDER and we know that these always fall into a single memory section. IOW, this patch here would result in overhead where it's not required to have that overhead. What am I missing and which scenario are we fixing? > > Signed-off-by: Chen Wandun > --- > mm/page_alloc.c | 16 +++++++++------- > 1 file changed, 9 insertions(+), 7 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 855211dea13e..758d8f069b32 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -721,7 +721,7 @@ static void prep_compound_head(struct page *page, unsigned int order) > > static void prep_compound_tail(struct page *head, int tail_idx) > { > - struct page *p = head + tail_idx; > + struct page *p = nth_page(head, tail_idx); > > p->mapping = TAIL_MAPPING; > set_compound_head(p, head); > @@ -1199,10 +1199,10 @@ static inline int check_free_page(struct page *page) > return 1; > } > > -static int free_tail_pages_check(struct page *head_page, struct page *page) > +static int free_tail_pages_check(struct page *head_page, int index) > { > + struct page *page = nth_page(head_page, index); > int ret = 1; > - > /* > * We rely page->lru.next never has bit 0 set, unless the page > * is PageTail(). Let's make sure that's true even for poisoned ->lru. > @@ -1213,7 +1213,7 @@ static int free_tail_pages_check(struct page *head_page, struct page *page) > ret = 0; > goto out; > } > - switch (page - head_page) { > + switch (index) { > case 1: > /* the first tail page: ->mapping may be compound_mapcount() */ > if (unlikely(compound_mapcount(page))) { > @@ -1322,6 +1322,7 @@ static __always_inline bool free_pages_prepare(struct page *page, > if (unlikely(order)) { > bool compound = PageCompound(page); > int i; > + struct page *tail_page; > > VM_BUG_ON_PAGE(compound && compound_order(page) != order, page); > > @@ -1330,13 +1331,14 @@ static __always_inline bool free_pages_prepare(struct page *page, > ClearPageHasHWPoisoned(page); > } > for (i = 1; i < (1 << order); i++) { > + tail_page = nth_page(page, i); > if (compound) > - bad += free_tail_pages_check(page, page + i); > - if (unlikely(check_free_page(page + i))) { > + bad += free_tail_pages_check(page, i); > + if (unlikely(check_free_page(tail_page))) { > bad++; > continue; > } > - (page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; > + tail_page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; > } > } > if (PageMappingFlags(page)) -- Thanks, David / dhildenb