Re: dd: avoid swap and benchmark of the nocache option

[Pádraig Brady]

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.