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Thu, 08 Dec 2022 10:03:15 -0800 (PST) Received: from localhost.localdomain ([198.13.51.166]) by smtp.gmail.com with ESMTPSA id x23-20020a63db57000000b004785e505bcdsm13377909pgi.51.2022.12.08.10.03.10 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 08 Dec 2022 10:03:15 -0800 (PST) From: Kairui Song To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Miaohe Lin , David Hildenbrand , "Huang, Ying" , Hugh Dickins , Kairui Song Subject: [PATCH 1/5] swapfile: get rid of volatile and avoid redundant read Date: Fri, 9 Dec 2022 02:02:05 +0800 Message-Id: <20221208180209.50845-2-ryncsn@gmail.com> X-Mailer: git-send-email 2.35.2 In-Reply-To: <20221208180209.50845-1-ryncsn@gmail.com> References: <20221208180209.50845-1-ryncsn@gmail.com> Reply-To: Kairui Song MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 9B48D1A0022 X-Stat-Signature: 5sti87nseqzwauridoybtrbk1q39nken X-HE-Tag: 1670522597-222098 X-HE-Meta: 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 lmViyYWY FX6srRXzyplJD7VSuWknxDzv58VzfUADQcrvN2dV44F0/NMYivh23jSWl0Pjv7oSzNkQk1LBnfv5XO38MGLG+SfKDDfD/0XFU/7h0sR0fLRk6LeQ5aWSqBG2Ic/1Uu8iiXxqzVMn2ULHWKArqqMXBLuIGwJxDNuo6PLa3b8dDwRBvxq26b3bkepIKvEMa75BFyJj2i3Tr7l/WYe36ffhKfB+1k/h57J93jfefipKGdjTLnKOs8B88Qe1wwDoQ4XtRVWYlU565+KVh9kG8lvcXJ22HvA== 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: 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 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; }