Re: [PATCH 4/4] mm: use the cached page for filemap_fault

[Andrew Morton]

On Fri, 30 Nov 2018 14:58:12 -0500 Josef Bacik <josef@xxxxxxxxxxxxxx> wrote:

> If we drop the mmap_sem we have to redo the vma lookup which requires
> redoing the fault handler.  Chances are we will just come back to the
> same page, so save this page in our vmf->cached_page and reuse it in the
> next loop through the fault handler.
> 

Is this really worthwhile?  Rerunning the fault handler is rare (we
hope) and a single pagecache lookup is fast.

Some performance testing results would be helpful here.  It's
practically obligatory when claiming a performance improvement.