On Fri, Feb 17, 2017 at 02:41:08PM +0900, Minchan Kim wrote:
> Hi Johannes,
>
> On Thu, Feb 16, 2017 at 01:40:18PM -0500, Johannes Weiner wrote:
> > On Tue, Feb 14, 2017 at 11:36:09AM -0800, Shaohua Li wrote:
> > > @@ -1419,11 +1419,18 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> > > VM_BUG_ON_PAGE(!PageSwapCache(page) && PageSwapBacked(page),
> > > page);
> > >
> > > - if (!PageDirty(page) && (flags & TTU_LZFREE)) {
> > > - /* It's a freeable page by MADV_FREE */
> > > - dec_mm_counter(mm, MM_ANONPAGES);
> > > - rp->lazyfreed++;
> > > - goto discard;
> > > + if (flags & TTU_LZFREE) {
> > > + if (!PageDirty(page)) {
> > > + /* It's a freeable page by MADV_FREE */
> > > + dec_mm_counter(mm, MM_ANONPAGES);
> > > + rp->lazyfreed++;
> > > + goto discard;
> > > + } else {
> > > + set_pte_at(mm, address, pvmw.pte, pteval);
> > > + ret = SWAP_FAIL;
> > > + page_vma_mapped_walk_done(&pvmw);
> > > + break;
> > > + }
> >
> > I don't understand why we need the TTU_LZFREE bit in general. More on
> > that below at the callsite.
>
> The reason I introduced it was ttu is used for migration/THP split path
> as well as reclaim. It's clear to discard them in reclaim path because
> it means surely memory pressure now but not sure with other path.
>
> If you guys think it's always win to discard them in try_to_unmap
> unconditionally, I think it would be better to be separate patch.
I was totally wrong.
Anon page with THP split/migration/HWPoison will not reach to discard path
in try_to_unmap_one so Johannes is right. We don't need TTU_LZFREE.
Sorry for the noise.
Thanks.
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