linux-kernel - Re: [PATCH 3/3] mm: when handling percpu_pagelist_fraction, use on_each

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Tue, 09 Apr 2013 12:27:07 -0700
From:	Cody P Schafer <cody@...ux.vnet.ibm.com>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm: when handling percpu_pagelist_fraction, use on_each_cpu()
 to set percpu pageset fields.

On 04/08/2013 11:06 PM, Gilad Ben-Yossef wrote:
> On Tue, Apr 9, 2013 at 9:03 AM, Gilad Ben-Yossef <gilad@...yossef.com> wrote:
>
>>
>>> I also wonder whether there could be unexpected interactions between ->high
>>> and ->batch not changing together atomically. For example, could adjusting
>>> this knob cause ->batch to rise enough that it is greater than the previous
>>> ->high? If the code above then runs with the previous ->high, ->count
>>> wouldn't be correct (checking this inside free_pcppages_bulk() might help on
>>> this one issue).
>>
>> You are right, but that can be treated in  setup_pagelist_highmark()  e.g.:
>>
>> 3993 static void setup_pagelist_highmark(struct per_cpu_pageset *p,
>> 3994                                 unsigned long high)
>> 3995 {
>> 3996         struct per_cpu_pages *pcp;
>>                  unsigned int batch;
>> 3997
>> 3998         pcp = &p->pcp;
>>                  /* We're about to mess with PCP in an non atomic fashion.
>>                     Put an intermediate safe value of batch and make sure it
>>                     is visible before any other change */
>>                  pcp->batch = 1UL;
>>                  smb_mb();
>>
>> 3999         pcp->high = high;
>
> and i think I missed another needed barrier here:
>                    smp_mb();
>
>>
>> 4000         batch = max(1UL, high/4);
>> 4001         if ((high/4) > (PAGE_SHIFT * 8))
>> 4002                 batch = PAGE_SHIFT * 8;
>>
>>                 pcp->batch = batch;
>> 4003 }
>>
>

Yep, that appears to work, provided no additional users of ->batch and 
->high show up. It seems we'll also need some locking to prevent 
concurrent updaters, but that is relatively light weight.

I'll roll up a new patchset that uses this methodology.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/