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[35.185.212.55]) by smtp.gmail.com with ESMTPSA id o10-20020a170902778a00b0015e8d4eb282sm9565242pll.204.2022.06.15.10.13.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jun 2022 10:13:58 -0700 (PDT) Date: Wed, 15 Jun 2022 10:13:55 -0700 From: Zach O'Keefe To: Miaohe Lin Cc: akpm@linux-foundation.org, aarcange@redhat.com, willy@infradead.org, vbabka@suse.cz, dhowells@redhat.com, neilb@suse.de, apopple@nvidia.com, david@redhat.com, surenb@google.com, peterx@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 7/7] mm/khugepaged: try to free transhuge swapcache when possible Message-ID: References: <20220611084731.55155-1-linmiaohe@huawei.com> <20220611084731.55155-8-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220611084731.55155-8-linmiaohe@huawei.com> ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655313241; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=NpbkGIIAT9U+dUlMWmDOrmdJZkG9VKb6160l0wJULSU=; b=I9bActVbJlFjFY2g5DdH8X/cltu7Gnnx6VtEuEORdb7X+4Gm4yz70GOZ3N4HKdlI3X82qM iLK7PGtTCHpb/qU3wUbyPlDf/xYZnoytpYJ3WDFUk1lJU/oTMceye9JLkJxAmTxt4gVbmx 4omr7TWOiPktoNgkjVWCY1YZwiT9t24= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655313241; a=rsa-sha256; cv=none; b=zVP4hA3uTVM2uqRc8/eCMB7tY8g524lgkKhKtGkbhpA14KpSBsZsSJ626p0A7J/WH0ZD7O wUowvU1/TsN05hnn2yuMSJ05bc08IsRMdiR4MW3Cs+fCo/5ZCewgtvtc4rW9QpuskjEXCx 4VG5ST5dQ5iJr+JK13bZbJew+ECGs08= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=IM78OQJN; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf18.hostedemail.com: domain of zokeefe@google.com designates 209.85.214.179 as permitted sender) smtp.mailfrom=zokeefe@google.com Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=IM78OQJN; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf18.hostedemail.com: domain of zokeefe@google.com designates 209.85.214.179 as permitted sender) smtp.mailfrom=zokeefe@google.com X-Rspamd-Server: rspam12 X-Rspam-User: X-Stat-Signature: mt663uia683gnzdj3dq8n8fh1b5rf3ky X-Rspamd-Queue-Id: 2EC801C0083 X-HE-Tag: 1655313241-524382 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 11 Jun 16:47, Miaohe Lin wrote: > Transhuge swapcaches won't be freed in __collapse_huge_page_copy(). > It's because release_pte_page() is not called for these pages and > thus free_page_and_swap_cache can't grab the page lock. These pages > won't be freed from swap cache even if we are the only user until > next time reclaim. It shouldn't hurt indeed, but we could try to > free these pages to save more memory for system. > > Signed-off-by: Miaohe Lin > --- > include/linux/swap.h | 5 +++++ > mm/khugepaged.c | 1 + > mm/swap.h | 5 ----- > 3 files changed, 6 insertions(+), 5 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 8672a7123ccd..ccb83b12b724 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -456,6 +456,7 @@ static inline unsigned long total_swapcache_pages(void) > return global_node_page_state(NR_SWAPCACHE); > } > > +extern void free_swap_cache(struct page *page); > extern void free_page_and_swap_cache(struct page *); > extern void free_pages_and_swap_cache(struct page **, int); > /* linux/mm/swapfile.c */ > @@ -540,6 +541,10 @@ static inline void put_swap_device(struct swap_info_struct *si) > /* used to sanity check ptes in zap_pte_range when CONFIG_SWAP=0 */ > #define free_swap_and_cache(e) is_pfn_swap_entry(e) > > +static inline void free_swap_cache(struct page *page) > +{ > +} > + > static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask) > { > return 0; > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index ee0a719c8be9..52109ad13f78 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -756,6 +756,7 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) { > list_del(&src_page->lru); > release_pte_page(src_page); > + free_swap_cache(src_page); > } > } Aside: in __collapse_huge_page_isolate() (and also here) why can't we just check PageCompound(page) && page == compound_head(page) to only act on compound pages once? AFAIK this would alleviate this compound_pagelist business.. Anyways, as-is, free_page_and_swap_cache() won't be able to do try_to_free_swap(), since it can't grab page lock, put it will call put_page(). I think (?) the last page ref might be dropped in release_pte_page(), so should free_swap_cache() come before it? > > diff --git a/mm/swap.h b/mm/swap.h > index 0193797b0c92..863f6086c916 100644 > --- a/mm/swap.h > +++ b/mm/swap.h > @@ -41,7 +41,6 @@ void __delete_from_swap_cache(struct page *page, > void delete_from_swap_cache(struct page *page); > void clear_shadow_from_swap_cache(int type, unsigned long begin, > unsigned long end); > -void free_swap_cache(struct page *page); > struct page *lookup_swap_cache(swp_entry_t entry, > struct vm_area_struct *vma, > unsigned long addr); > @@ -81,10 +80,6 @@ static inline struct address_space *swap_address_space(swp_entry_t entry) > return NULL; > } > > -static inline void free_swap_cache(struct page *page) > -{ > -} > - > static inline void show_swap_cache_info(void) > { > } > -- > 2.23.0 > >