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Re: dd: avoid swap and benchmark of the nocache option
From: |
Pádraig Brady |
Subject: |
Re: dd: avoid swap and benchmark of the nocache option |
Date: |
Tue, 12 Jan 2016 11:19:07 +0000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 11/01/16 23:19, Francois wrote:
> On 11 January 2016 at 23:55, Pádraig Brady <address@hidden> wrote:
>> On 11/01/16 21:59, Francois wrote:
>
>>> - and maybe that we can do a better use of posix_advise.
>>
>> What do you mean for that do do exactly?
>
> nocache limits itself to advising a single buffer, while what we really
> want is to tell the kernel it's really the full file we don't need in
> cache. Doing a ADV_DONTNEED starting from offset 0 each time
> drastically reduce the number of pages put into cache, and completely
> removes swapping, and this *without sync*.
Right. But didn't doing that take 300% more "sys" time,
while not providing much benefits over oflag=nocache,sync ?
thanks,
Pádraig.