Re: [PATCH] mm/gup: don't check page lru flag before draining it

[yangge1116]

在 2024/6/12 下午3:32, David Hildenbrand 写道:
> On 11.06.24 13:20, yangge1116 wrote:
> > 在 2024/6/9 上午12:03, David Hildenbrand 写道:
> > > On 08.06.24 17:15, Matthew Wilcox wrote:
> > > > On Sat, Jun 08, 2024 at 12:38:49PM +0800, yangge1116 wrote:
> > > > > Can we add a PG_lru_batch flag to determine whether a page is in lru
> > > > > batch?
> > > > > If we can, seems this problem will be easier.
> > > >
> > > > Page flags are in short supply.  You'd need a really good 
> > > > justification.
> > >
> > > A flag would not be able to handle the "part of multiple LRU batches"
> > > that should currently possible (when to clear the flag?). Well, if we
> > > have to keep supporting that. If we only to be part in a single LRU
> > > batch, a new flag could work and we could still allow isolating a folio
> > > from LRU while in some LRU batch.
> >
> > Yes, before adding a folio to LRU batch, check whether the folio has
> > been added. Add the folio to LRU batch only if the folio has not been
> > added.
> >
> > > If we could handle it using the existing flags, that would of course be
> > > better (wondering if we could store more information in the existing
> > > flags by using a different encoding for the different states).
> >
> > If a folio contains more than one page, the folio will not be added to
> > LRU batch. Can we use folio_test_large(folio) to filter?
> >
> > if (!folio_test_large(folio) && drain_allow) {
> >     lru_add_drain_all();
> >     drain_allow = false;
> > }
>
> I think we should do better than this, and not do arbitrary 
> lru_add_drain_all() calls.

Thanks, I will prepare the V2.