Re: [Bug-tar] Use posix_fadvise to improve archive creation performance

[Mark]

On Thu, March 30, 2017 16:08, Paul Eggert wrote:
> On 03/29/2017 04:32 PM, Carlo Alberto Ferraris wrote:
>> The change itself should be pretty safe
>
> Alas, I've run into setups where using POSIX_FADV_SEQUENTIAL and
> POSIX_FADV_DONTNEED slow things down. See, for example:
>
> https://github.com/jborg/attic/issues/252
>
> Also, if we're going to use these flags, shouldn't it be
> POSIX_FADV_NOREUSE instead of POSIX_FADV_DONTNEED? And shouldn't the
> size be 0?

Carlo's revised patch doesn't use POSIX_FADV_DONTNEED. (It only uses
POSIX_FADV_SEQUENTIAL and POSIX_FADV_WILLNEED.)

As mentioned POSIX_FADV_NOREUSE is a no-op on Linux.

I think it would be a good idea to add an option to tell tar whether to
use POSIX_FADV_NOREUSE, POSIX_FADV_DONTNEED, or neither, since there may
be cases where any of the three possibilities is best. Or maybe tar could
read an environment variable to determine which to use?