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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id o1-20020ac841c1000000b0039cc82a319asm8947073qtm.76.2022.12.04.20.14.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 04 Dec 2022 20:14:03 -0800 (PST) Date: Sun, 4 Dec 2022 20:13:53 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Chen Wandun cc: akpm@linux-foundation.org, shli@kernel.org, hughd@google.com, arnd@arndb.de, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] swapfile: fix uncorrect statistical count about free swap In-Reply-To: <20221205024726.3111808-1-chenwandun@huawei.com> Message-ID: References: <20221205024726.3111808-1-chenwandun@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Spamd-Result: default: False [-0.25 / 9.00]; BAYES_HAM(-3.35)[92.97%]; SORBS_IRL_BL(3.00)[209.85.222.170:from]; MIME_GOOD(-0.10)[text/plain]; RCVD_NO_TLS_LAST(0.10)[]; BAD_REP_POLICIES(0.10)[]; TO_DN_SOME(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; DMARC_POLICY_ALLOW(0.00)[google.com,reject]; DKIM_TRACE(0.00)[google.com:+]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; R_SPF_ALLOW(0.00)[+ip4:209.85.128.0/17]; RCVD_COUNT_THREE(0.00)[3]; R_DKIM_ALLOW(0.00)[google.com:s=20210112]; ARC_SIGNED(0.00)[hostedemail.com:s=arc-20220608:i=1]; PREVIOUSLY_DELIVERED(0.00)[linux-mm@kvack.org]; RCVD_VIA_SMTP_AUTH(0.00)[] X-Rspamd-Queue-Id: BC61E40011 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: 6sxoywz1qw5s1xig9gtb5zf4nr1yanbf X-HE-Tag: 1670213644-621325 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 Mon, 5 Dec 2022, Chen Wandun wrote: > The counter of free swap turn to negtive during swapoff, this > phenomenon can be observed in oom log, such as: > > 1226 total pagecache pages > 47 pages in swap cache > Swap cache stats: add 119633, delete 119814, find 26832/82125 > Free swap = -31796kB > Total swap = 0kB > 1048576 pages RAM > > Subtract the size of swap partition from free swap should put behind > try_to_unuse, otherwise, it will result in negtive counter if swap > partition is in use. > > Fixes: ec8acf20afb8 ("swap: add per-partition lock for swapfile") > Signed-off-by: Chen Wandun No: it is intentional, and long established, that the count goes negative during swapoff - that helps to inform you that it is in swapoff. Hugh > --- > mm/swapfile.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 72e481aacd5d..5b9b695be84b 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -2316,8 +2316,6 @@ static void setup_swap_info(struct swap_info_struct *p, int prio, > static void _enable_swap_info(struct swap_info_struct *p) > { > p->flags |= SWP_WRITEOK; > - atomic_long_add(p->pages, &nr_swap_pages); > - total_swap_pages += p->pages; > > assert_spin_locked(&swap_lock); > /* > @@ -2353,6 +2351,8 @@ static void enable_swap_info(struct swap_info_struct *p, int prio, > spin_lock(&swap_lock); > spin_lock(&p->lock); > _enable_swap_info(p); > + atomic_long_add(p->pages, &nr_swap_pages); > + total_swap_pages += p->pages; > spin_unlock(&p->lock); > spin_unlock(&swap_lock); > } > @@ -2444,8 +2444,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) > least_priority++; > } > plist_del(&p->list, &swap_active_head); > - atomic_long_sub(p->pages, &nr_swap_pages); > - total_swap_pages -= p->pages; > p->flags &= ~SWP_WRITEOK; > spin_unlock(&p->lock); > spin_unlock(&swap_lock); > @@ -2500,6 +2498,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) > spin_lock(&p->lock); > } > > + atomic_long_sub(p->pages, &nr_swap_pages); > + total_swap_pages -= p->pages; > swap_file = p->swap_file; > old_block_size = p->old_block_size; > p->swap_file = NULL; > -- > 2.25.1 > >