From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4A587C43461 for ; Fri, 11 Sep 2020 03:38:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1B68521D7E for ; Fri, 11 Sep 2020 03:38:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725845AbgIKDi6 (ORCPT ); Thu, 10 Sep 2020 23:38:58 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:49712 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725648AbgIKDiz (ORCPT ); Thu, 10 Sep 2020 23:38:55 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R181e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04423;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=22;SR=0;TI=SMTPD_---0U8YuYvo_1599795527; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0U8YuYvo_1599795527) by smtp.aliyun-inc.com(127.0.0.1); Fri, 11 Sep 2020 11:38:49 +0800 Subject: Re: [PATCH v18 06/32] mm/thp: narrow lru locking To: Matthew Wilcox Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, tj@kernel.org, hughd@google.com, khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com, hannes@cmpxchg.org, lkp@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, shakeelb@google.com, iamjoonsoo.kim@lge.com, richard.weiyang@gmail.com, kirill@shutemov.name, alexander.duyck@gmail.com, rong.a.chen@intel.com, mhocko@suse.com, vdavydov.dev@gmail.com, shy828301@gmail.com, Andrea Arcangeli References: <1598273705-69124-1-git-send-email-alex.shi@linux.alibaba.com> <1598273705-69124-7-git-send-email-alex.shi@linux.alibaba.com> <20200910134923.GR6583@casper.infradead.org> From: Alex Shi Message-ID: <514f6afa-dbf7-11c5-5431-1d558d2c20c9@linux.alibaba.com> Date: Fri, 11 Sep 2020 11:37:50 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200910134923.GR6583@casper.infradead.org> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ÔÚ 2020/9/10 ÏÂÎç9:49, Matthew Wilcox дµÀ: > On Mon, Aug 24, 2020 at 08:54:39PM +0800, Alex Shi wrote: >> lru_lock and page cache xa_lock have no reason with current sequence, >> put them together isn't necessary. let's narrow the lru locking, but >> left the local_irq_disable to block interrupt re-entry and statistic update. > > What stats are you talking about here? Hi Matthew, Thanks for comments! like __dec_node_page_state(head, NR_SHMEM_THPS); will have preemptive warning... > >> +++ b/mm/huge_memory.c >> @@ -2397,7 +2397,7 @@ static void __split_huge_page_tail(struct page *head, int tail, >> } >> >> static void __split_huge_page(struct page *page, struct list_head *list, >> - pgoff_t end, unsigned long flags) >> + pgoff_t end) > > Please don't change this whitespace. It's really annoying having to > adjust the whitespace when renaming a function. Just two tabs indentation > to give a clear separation of arguments from code is fine. > > > How about this patch instead? It occurred to me we already have > perfectly good infrastructure to track whether or not interrupts are > already disabled, and so we should use that instead of ensuring that > interrupts are disabled, or tracking that ourselves. So your proposal looks like; 1, xa_lock_irq(&mapping->i_pages); (optional) 2, spin_lock_irqsave(&ds_queue->split_queue_lock, flags); 3, spin_lock_irqsave(&pgdat->lru_lock, flags); Is there meaningful for the 2nd and 3rd flags? IIRC, I had a similar proposal as your, the flags used in xa_lock_irqsave(), but objected by Hugh. Thanks Alex > > But I may have missed something else that's relying on having > interrupts disabled. Please check carefully. > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 2ccff8472cd4..74cae6c032f9 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2376,17 +2376,16 @@ static void __split_huge_page_tail(struct page *head, int tail, > } > > static void __split_huge_page(struct page *page, struct list_head *list, > - pgoff_t end, unsigned long flags) > + pgoff_t end) > { > struct page *head = compound_head(page); > pg_data_t *pgdat = page_pgdat(head); > struct lruvec *lruvec; > struct address_space *swap_cache = NULL; > unsigned long offset = 0; > + unsigned long flags; > int i; > > - lruvec = mem_cgroup_page_lruvec(head, pgdat); > - > /* complete memcg works before add pages to LRU */ > mem_cgroup_split_huge_fixup(head); > > @@ -2395,9 +2394,13 @@ static void __split_huge_page(struct page *page, struct list_head *list, > > offset = swp_offset(entry); > swap_cache = swap_address_space(entry); > - xa_lock(&swap_cache->i_pages); > + xa_lock_irq(&swap_cache->i_pages); > } > > + /* prevent PageLRU to go away from under us, and freeze lru stats */ > + spin_lock_irqsave(&pgdat->lru_lock, flags); > + lruvec = mem_cgroup_page_lruvec(head, pgdat); > + > for (i = HPAGE_PMD_NR - 1; i >= 1; i--) { > __split_huge_page_tail(head, i, lruvec, list); > /* Some pages can be beyond i_size: drop them from page cache */ > @@ -2417,6 +2420,7 @@ static void __split_huge_page(struct page *page, struct list_head *list, > } > > ClearPageCompound(head); > + spin_unlock_irqrestore(&pgdat->lru_lock, flags); > > split_page_owner(head, HPAGE_PMD_ORDER); > > @@ -2425,18 +2429,16 @@ static void __split_huge_page(struct page *page, struct list_head *list, > /* Additional pin to swap cache */ > if (PageSwapCache(head)) { > page_ref_add(head, 2); > - xa_unlock(&swap_cache->i_pages); > + xa_unlock_irq(&swap_cache->i_pages); > } else { > page_ref_inc(head); > } > } else { > /* Additional pin to page cache */ > page_ref_add(head, 2); > - xa_unlock(&head->mapping->i_pages); > + xa_unlock_irq(&head->mapping->i_pages); > } > > - spin_unlock_irqrestore(&pgdat->lru_lock, flags); > - > remap_page(head); > > for (i = 0; i < HPAGE_PMD_NR; i++) { > @@ -2574,7 +2576,6 @@ bool can_split_huge_page(struct page *page, int *pextra_pins) > int split_huge_page_to_list(struct page *page, struct list_head *list) > { > struct page *head = compound_head(page); > - struct pglist_data *pgdata = NODE_DATA(page_to_nid(head)); > struct deferred_split *ds_queue = get_deferred_split_queue(head); > struct anon_vma *anon_vma = NULL; > struct address_space *mapping = NULL; > @@ -2640,9 +2641,6 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > unmap_page(head); > VM_BUG_ON_PAGE(compound_mapcount(head), head); > > - /* prevent PageLRU to go away from under us, and freeze lru stats */ > - spin_lock_irqsave(&pgdata->lru_lock, flags); > - > if (mapping) { > XA_STATE(xas, &mapping->i_pages, page_index(head)); > > @@ -2650,13 +2648,13 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > * Check if the head page is present in page cache. > * We assume all tail are present too, if head is there. > */ > - xa_lock(&mapping->i_pages); > + xa_lock_irq(&mapping->i_pages); > if (xas_load(&xas) != head) > goto fail; > } > > /* Prevent deferred_split_scan() touching ->_refcount */ > - spin_lock(&ds_queue->split_queue_lock); > + spin_lock_irqsave(&ds_queue->split_queue_lock, flags); > count = page_count(head); > mapcount = total_mapcount(head); > if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) { > @@ -2664,7 +2662,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > ds_queue->split_queue_len--; > list_del(page_deferred_list(head)); > } > - spin_unlock(&ds_queue->split_queue_lock); > + spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags); > if (mapping) { > if (PageSwapBacked(head)) > __dec_node_page_state(head, NR_SHMEM_THPS); > @@ -2672,7 +2670,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > __dec_node_page_state(head, NR_FILE_THPS); > } > > - __split_huge_page(page, list, end, flags); > + __split_huge_page(page, list, end); > if (PageSwapCache(head)) { > swp_entry_t entry = { .val = page_private(head) }; > > @@ -2688,10 +2686,9 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > dump_page(page, "total_mapcount(head) > 0"); > BUG(); > } > - spin_unlock(&ds_queue->split_queue_lock); > + spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags); > fail: if (mapping) > - xa_unlock(&mapping->i_pages); > - spin_unlock_irqrestore(&pgdata->lru_lock, flags); > + xa_unlock_irq(&mapping->i_pages); > remap_page(head); > ret = -EBUSY; > } >