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X-IronPort-AV: E=McAfee;i="6500,9779,10555"; a="381673153" X-IronPort-AV: E=Sophos;i="5.96,228,1665471600"; d="scan'208";a="381673153" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2022 18:49:55 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10555"; a="710736287" X-IronPort-AV: E=Sophos;i="5.96,228,1665471600"; d="scan'208";a="710736287" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2022 18:49:52 -0800 From: "Huang, Ying" To: Kairui Song Cc: linux-mm@kvack.org, Kairui Song , linux-kernel@vger.kernel.org, Andrew Morton , Miaohe Lin , David Hildenbrand , Hugh Dickins Subject: Re: [PATCH 1/5] swapfile: get rid of volatile and avoid redundant read References: <20221208180209.50845-1-ryncsn@gmail.com> <20221208180209.50845-2-ryncsn@gmail.com> Date: Fri, 09 Dec 2022 10:48:41 +0800 In-Reply-To: <20221208180209.50845-2-ryncsn@gmail.com> (Kairui Song's message of "Fri, 9 Dec 2022 02:02:05 +0800") Message-ID: <874ju5s35i.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 15447180010 X-Stat-Signature: s7aig8pmrggtrqgaa8ige99fy5fsh9ti X-HE-Tag: 1670554196-631999 X-HE-Meta: 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 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: Kairui Song writes: > From: Kairui Song > > Convert a volatile variable to more readable READ_ONCE. And this > actually avoids the code from reading the variable twice redundantly > when it races. > > Signed-off-by: Kairui Song LGTM, Thanks! Reviewed-by: "Huang, Ying" > --- > mm/swapfile.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 72e481aacd5d..ff4f3cb85232 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -1836,13 +1836,13 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > pte_t *pte; > struct swap_info_struct *si; > int ret = 0; > - volatile unsigned char *swap_map; > > si = swap_info[type]; > pte = pte_offset_map(pmd, addr); > do { > struct folio *folio; > unsigned long offset; > + unsigned char swp_count; > > if (!is_swap_pte(*pte)) > continue; > @@ -1853,7 +1853,6 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > > offset = swp_offset(entry); > pte_unmap(pte); > - swap_map = &si->swap_map[offset]; > folio = swap_cache_get_folio(entry, vma, addr); > if (!folio) { > struct page *page; > @@ -1870,8 +1869,10 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > folio = page_folio(page); > } > if (!folio) { > - if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD) > + swp_count = READ_ONCE(si->swap_map[offset]); > + if (swp_count == 0 || swp_count == SWAP_MAP_BAD) > goto try_next; > + > return -ENOMEM; > }