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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 9373CC2BB54 for ; Tue, 7 Apr 2020 11:33:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 73C0E2063A for ; Tue, 7 Apr 2020 11:33:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728368AbgDGLdw (ORCPT ); Tue, 7 Apr 2020 07:33:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:47780 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728023AbgDGLdw (ORCPT ); Tue, 7 Apr 2020 07:33:52 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id D35EAABD7; Tue, 7 Apr 2020 11:33:48 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 589C61E1233; Tue, 7 Apr 2020 13:33:48 +0200 (CEST) Date: Tue, 7 Apr 2020 13:33:48 +0200 From: Jan Kara To: Michal Hocko Cc: Jan Kara , NeilBrown , Trond Myklebust , "Anna.Schumaker@Netapp.com" , Andrew Morton , linux-mm@kvack.org, linux-nfs@vger.kernel.org, LKML Subject: Re: [PATCH 2/2] MM: Discard NR_UNSTABLE_NFS, use NR_WRITEBACK instead. Message-ID: <20200407113348.GG9482@quack2.suse.cz> References: <878sj8w55y.fsf@notabene.neil.brown.name> <20200407102515.GB9482@quack2.suse.cz> <20200407112412.GO18914@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200407112412.GO18914@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 07-04-20 13:24:12, Michal Hocko wrote: > On Tue 07-04-20 12:25:15, Jan Kara wrote: > > > @@ -1707,8 +1706,16 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos) > > > static void *vmstat_next(struct seq_file *m, void *arg, loff_t *pos) > > > { > > > (*pos)++; > > > - if (*pos >= NR_VMSTAT_ITEMS) > > > + if (*pos >= NR_VMSTAT_ITEMS) { > > > + /* > > > + * Deprecated counters which are no longer represented > > > + * in vmstat arrays. We just lie about them to be always > > > + * 0 to not break userspace which might expect them in > > > + * the output. > > > + */ > > > + seq_puts(m, "nr_unstable 0"); > > > return NULL; > > > + } > > > return (unsigned long *)m->private + *pos; > > > } > > > > Umm, how is this supposed to work? vmstat_next() should return next element > > of the sequence, not fill anything into seq_file - that's the job of > > vmstat_show(). Looking at seq_read() implementation it may actually end up > > working fine but I wouldn't really bet much on it especially in corner > > cases like when we are just about to fill the user buffer and then need to > > restart reading close to an end of vmstat file or so. > > Well, I have to confess I haven't really tested this myself but the > logic was to have this output close to NR_VMSTAT_ITEMS break out of > the counters loop. > > > Michal, won't it be cleaner to have NR_VM_DEPRECATED_ITEMS included in > > NR_VMSTAT_ITEMS, have names of these items in vmstat_text, and just set > > appropriate number of 0 entries at the end of the array generated in > > vmstat_start() and be done with it? That seems conceptually simpler and the > > overhead is minimal. > > Yes, that would be much nicer, albeit more code. So I believe you meant > something like this? > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 462f6873905a..a18611197bea 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -237,7 +237,6 @@ enum node_stat_item { > NR_FILE_THPS, > NR_FILE_PMDMAPPED, > NR_ANON_THPS, > - NR_UNSTABLE_NFS, /* NFS unstable pages */ > NR_VMSCAN_WRITE, > NR_VMSCAN_IMMEDIATE, /* Prioritise for reclaim when writeback ends */ > NR_DIRTIED, /* page dirtyings since bootup */ > diff --git a/mm/vmstat.c b/mm/vmstat.c > index 78d53378db99..992e162f1886 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -1162,7 +1162,6 @@ const char * const vmstat_text[] = { > "nr_file_hugepages", > "nr_file_pmdmapped", > "nr_anon_transparent_hugepages", > - "nr_unstable", > "nr_vmscan_write", > "nr_vmscan_immediate_reclaim", > "nr_dirtied", > @@ -1293,9 +1292,13 @@ const char * const vmstat_text[] = { > "swap_ra_hit", > #endif > #endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */ > + /* Deprecated counters. Count them in NR_VM_DEPRECATED_ITEMS */ > + "nr_unstable", > }; > #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */ > > +#define NR_VM_DEPRECATED_ITEMS 1 > + > #if (defined(CONFIG_DEBUG_FS) && defined(CONFIG_COMPACTION)) || \ > defined(CONFIG_PROC_FS) > static void *frag_start(struct seq_file *m, loff_t *pos) > @@ -1661,7 +1664,8 @@ static const struct seq_operations zoneinfo_op = { > NR_VM_NODE_STAT_ITEMS + \ > NR_VM_WRITEBACK_STAT_ITEMS + \ > (IS_ENABLED(CONFIG_VM_EVENT_COUNTERS) ? \ > - NR_VM_EVENT_ITEMS : 0)) > + NR_VM_EVENT_ITEMS : 0) + \ > + NR_VM_DEPRECATED_ITEMS) > > static void *vmstat_start(struct seq_file *m, loff_t *pos) > { > @@ -1698,7 +1702,11 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos) > all_vm_events(v); > v[PGPGIN] /= 2; /* sectors -> kbytes */ > v[PGPGOUT] /= 2; > + v += NR_VM_EVENT_ITEMS; > #endif > + for (i = 0; i < NR_VM_DEPRECATED_ITEMS) ^^ ; i++ here but otherwise yes, this is what I meant. Thanks! > + v[i] = 0; > + > return (unsigned long *)m->private + *pos; > } Honza -- Jan Kara SUSE Labs, CR