Re: [PATCH 1/2] mm: fadvise: fix POSIX_FADV_DONTNEED

[Dave Hansen <dave@linux.vnet.ibm.com>]

On 02/23/2013 07:37 PM, Phillip Susi wrote:
> This is the correct behavior prescribed by posix.  If you have been
> using it for that purpose in the past, then you were using the wrong
> syscall.  If you want to begin writeout now, then you should be using
> sync_file_range().  As it was, it only initiated writeout if the
> backing device was not already congested, which is going to no longer
> be the case rather soon if you ( or other tasks ) are writing
> significant amounts of data.
> 
> If you really want to stay out of memory reclaim entirely, then you
> should be using O_DIRECT.

These are folks that want to use the page cache, but also want to be in
control of when it gets written out (sync_file_range() is used) and when
it goes away.  Sure, they can use O_DIRECT and do all of the buffering
internally, but that means changing the application.

I actually really like the concept behind your patch.  It looks like
very useful functionality.  I'm just saying that I know it will break
_existing_ users.

I'm actually in the process of _trying_ to extricate this particular app
from handling their own reclaim management entirely.  Your patch looks
like a nice part of the puzzle.

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