On Fri, 26 Jun 2015 10:47:39 -0400
nick <[email protected]> wrote:
>
>
> On 2015-06-26 09:56 AM, Dominik Dingel wrote:
> > On Thu, 25 Jun 2015 21:36:37 -0400
> > Nicholas Krause <[email protected]> wrote:
> >
> >> This adds a return check after the call to the function rmap_walk
> >> in the function page_referenced as this function call can fail
> >> and thus should signal callers of page_referenced if this happens
> >> by returning the SWAP macro return value as returned by rmap_walk
> >> here. In addition also check if have locked the page pointer as
> >> passed to this particular and unlock it with unlock_page if this
> >> page is locked before returning our SWAP marco return code from
> >> rmap_walk.
> >>
> >> Signed-off-by: Nicholas Krause <[email protected]>
> >> ---
> >> mm/rmap.c | 10 +++++++++-
> >> 1 file changed, 9 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/mm/rmap.c b/mm/rmap.c
> >> index 171b687..e4df848 100644
> >> --- a/mm/rmap.c
> >> +++ b/mm/rmap.c
> >> @@ -814,7 +814,9 @@ static bool invalid_page_referenced_vma(struct vm_area_struct *vma, void *arg)
> >> * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
> >> *
> >> * Quick test_and_clear_referenced for all mappings to a page,
> >> - * returns the number of ptes which referenced the page.
> >> + * returns the number of ptes which referenced the page.On
> >> + * error returns either zero or the error code returned from
> >> + * the failed call to rmap_walk.
> >> */
> >> int page_referenced(struct page *page,
> >> int is_locked,
> >> @@ -855,7 +857,13 @@ int page_referenced(struct page *page,
> >> rwc.invalid_vma = invalid_page_referenced_vma;
> >> }
> >>
> >> +
> >
> > unnecessary empty line
> >
> >> ret = rmap_walk(page, &rwc);
> >> + if (!ret) {
> >> + if (we_locked)
> >> + unlock_page(page);
> >> + return ret;
> >> + }
> >
> > I don't see why the function should propagate the rmap_walk return value.
> > rmap_walk will not set pra.referenced, so that both callers just skip.
> >
> > What is the purpose of the given patch? Do you have any real case introducing such code,
> > which is imho incomplete as all callers need to take care of the changed return value!
> >
> There is only one caller that needs to be moved over if this case is put in. Further more
> do we care if executing rmap_walk fails as if it does this means we were unable to execute
> the function page_referenced one on the rmap_walk_control structure rwc and this can be
> a issue in my option, if not then we can just remove the ret variable and execute rmap_walk
> without checking it's return value.
> Cheers Nick
Let me rephrase: what will happen after you return ret?
What will:
- shrink_active_list
- page_check_references
now do?
For your second thinking it would be good to check how and why ret was introduced?
git log -L '/int page_referenced(/',/^}/:mm/rmap.c