linux-kernel - Re: [PATCH 1/4] mm: migrate: use a folio in add_page_for

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Message-ID: <ZMud3RreEpsvFKuA@casper.infradead.org>
Date:   Thu, 3 Aug 2023 13:30:21 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Huang Ying <ying.huang@...el.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH 1/4] mm: migrate: use a folio in add_page_for_migration()

On Thu, Aug 03, 2023 at 03:13:21PM +0800, Kefeng Wang wrote:
> 
> 
> On 2023/8/2 20:21, Matthew Wilcox wrote:
> > On Wed, Aug 02, 2023 at 05:53:43PM +0800, Kefeng Wang wrote:
> > >   	err = -EACCES;
> > > -	if (page_mapcount(page) > 1 && !migrate_all)
> > > -		goto out_putpage;
> > > +	if (folio_estimated_sharers(folio) > 1 && !migrate_all)
> > > +		goto out_putfolio;
> > 
> > I do not think this is the correct change.  Maybe leave this line
> > alone.
> 
> Ok, I am aware of the discussion about this in other mail, will not
> change it(also the next two patch about this function), or wait the
> new work of David.
> > 
> > > -	if (PageHuge(page)) {
> > > -		if (PageHead(page)) {
> > > -			isolated = isolate_hugetlb(page_folio(page), pagelist);
> > > +	if (folio_test_hugetlb(folio)) {
> > > +		if (folio_test_large(folio)) {
> > 
> > This makes no sense when you read it.  All hugetlb folios are large,
> > by definition.  Think about what this code used to do, and what it
> > should be changed to.
> 
> hugetlb folio is self large folio, will drop redundant check

No, that's not the difference.  Keep thinking about it.  This is not
a mechanical translation!