linux-kernel - Re: [PATCH RFC 0/4] mm/ksm: add option to automerge VMAs

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Message-ID: <20190513120631.cm2mc5grkofvloyk@butterfly.localdomain>
Date:   Mon, 13 May 2019 14:06:31 +0200
From:   Oleksandr Natalenko <oleksandr@...hat.com>
To:     Timofey Titovets <nefelim4ag@...il.com>
Cc:     Kirill Tkhai <ktkhai@...tuozzo.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Aaron Tomlin <atomlin@...hat.com>, linux-mm@...ck.org
Subject: Re: [PATCH RFC 0/4] mm/ksm: add option to automerge VMAs

On Mon, May 13, 2019 at 02:01:17PM +0200, Oleksandr Natalenko wrote:
> On Mon, May 13, 2019 at 02:48:29PM +0300, Timofey Titovets wrote:
> > > Also, just for the sake of another piece of stats here:
> > >
> > > $ echo "$(cat /sys/kernel/mm/ksm/pages_sharing) * 4 / 1024" | bc
> > > 526
> > 
> > IIRC, for calculate saving you must use (pages_shared - pages_sharing)
> 
> Based on Documentation/ABI/testing/sysfs-kernel-mm-ksm:
> 
> 	pages_shared: how many shared pages are being used.
> 
> 	pages_sharing: how many more sites are sharing them i.e. how
> 	much saved.
> 
> and unless I'm missing something, this must be already accounted:
> 
> [~]$ echo "$(cat /sys/kernel/mm/ksm/pages_shared) * 4 / 1024" | bc
> 69
> 
> [~]$ echo "$(cat /sys/kernel/mm/ksm/pages_sharing) * 4 / 1024" | bc
> 563

Yup. To expand on this,

 246 /* The number of nodes in the stable tree */
 247 static unsigned long ksm_pages_shared;
 248 
 249 /* The number of page slots additionally sharing those nodes */
 250 static unsigned long ksm_pages_sharing;

2037     if (rmap_item->hlist.next)
2038         ksm_pages_sharing++;
2039     else
2040         ksm_pages_shared++;

IOW, first item is accounter in "shared", the rest will go to "sharing".

-- 
  Best regards,
    Oleksandr Natalenko (post-factum)
    Senior Software Maintenance Engineer