Re: [PATCH] mm/filemap.c: unconditionally call mark_page_accessed

Andrew Morton
2007-03-15T22:08:06Z

On Thu, 15 Mar 2007 22:49:23 +0100
Andrea Arcangeli <andrea@suse.de> wrote:

> On Thu, Mar 15, 2007 at 11:07:35AM -0800, Andrew Morton wrote:
> > > On Thu, 15 Mar 2007 01:22:45 -0400 (EDT) Ashif Harji <asharji@cs.uwaterloo.ca> wrote:
> > > I still think the simple fix of removing the
> > > condition is the best approach, but I'm certainly open to alternatives.
> >
> > Yes, the problem of falsely activating pages when the file is read in small
> > hunks is worse than the problem which your patch fixes.
>
> Really? I would have expected all performance sensitive apps to read
> in >=PAGE_SIZE chunks. And if they don't because they split their
> dataset in blocks (like some database), it may not be so wrong to
> activate those pages that have two "hot" blocks more aggressively than
> those pages with a single hot block.

But the problem which is being fixed here is really obscure: an application
repeatedly reading the first page and only the first page of a file, always
via the same fd.

I'd expect that the sub-page-size read scenarion happens heaps more often
than that, especially when dealing with larger PAGE_SIZEs.