Messages in this thread | | | Date | Mon, 3 Mar 2014 15:29:00 -0800 | Subject | Re: [PATCH 0/1] mm, shmem: map few pages around fault address if they are in page cache | From | Linus Torvalds <> |
| |
On Mon, Mar 3, 2014 at 2:38 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > > When the file is uncached, results are peculiar: > > 0.00user 2.84system 0:50.90elapsed 5%CPU (0avgtext+0avgdata 4198096maxresident)k > 0inputs+0outputs (1major+49666minor)pagefaults 0swaps > > That's approximately 3x more minor faults.
This is not peculiar.
When the file is uncached, some pages will obviously be under IO due to readahead etc. And the fault-around code very much on purpose will *not* try to wait for those pages, so any busy pages will just simply not be faulted-around.
So you should still have fewer minor faults than faulting on *every* page (ie the non-fault-around case), but I would very much expect that fault-around will not see the full "one sixteenth" reduction in minor faults.
And the order of IO will not matter, since the read-ahead is asynchronous wrt the page-faults.
Linus
| |