Re: [PATCH] mm: thp: don't need drain lru cache when splitting and mlocking THP

[Yang Shi]

On 4/2/20 4:04 PM, Daniel Jordan wrote:
> On Sat, Mar 28, 2020 at 03:29:40AM +0800, Yang Shi wrote:
> > Since the commit 8f182270dfec ("mm/swap.c: flush lru pvecs on compound
> > page arrival") THP would not stay in pagevec anymore.  So the
> > optimization made by commit d965432234db ("thp: increase
> > split_huge_page() success rate") doesn't make sense anymore, which tries
> > to unpin munlocked THPs from pagevec by draining pagevec.
> >
> > And draining lru cache before isolating THP in mlock path is unnecessary
> > either.
> Can we get some of that nice history in this part too?
>
> Draining lru cache before isolating THP in mlock path is also unnecessary.
> b676b293fb48 ("mm, thp: fix mapped pages avoiding unevictable list on mlock")
> added it and 9a73f61bdb8a ("thp, mlock: do not mlock PTE-mapped file huge
> pages") accidentally carried it over after the above optimization went in.

Thanks for finding out this, I didn't dig that far. Will add it into v2.

> > Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> > Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> Since we don't mlock pte-mapped THP, it seems these huge pages wouldn't ever be
> in the pagevecs if I'm understanding it all.

Yes, it is correct.

> Saves lines and some amount of overhead and lru contention, so looks good.
>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>

Thanks.