linux-kernel - Re: [PATCH mm-unstable 8/8] mm/hugetlb: convert demote_free_huge

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Date:   Mon, 9 Jan 2023 10:23:46 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc:     Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        songmuchun@...edance.com, tsahu@...ux.ibm.com, jhubbard@...dia.com
Subject: Re: [PATCH mm-unstable 8/8] mm/hugetlb: convert
 demote_free_huge_page to folios

On 01/09/23 10:36, Sidhartha Kumar wrote:
> On 1/7/23 2:55 PM, Mike Kravetz wrote:
> > On 01/07/23 01:31, Matthew Wilcox wrote:
> > > On Fri, Jan 06, 2023 at 05:11:36PM -0800, Mike Kravetz wrote:
> > > > On 01/03/23 13:13, Sidhartha Kumar wrote:
> > > > > @@ -3477,15 +3477,15 @@ static int demote_free_huge_page(struct hstate *h, struct page *page)
> > > > >   	mutex_lock(&target_hstate->resize_lock);
> > > > >   	for (i = 0; i < pages_per_huge_page(h);
> > > > >   				i += pages_per_huge_page(target_hstate)) {
> > > > > -		subpage = nth_page(page, i);
> > > > > -		folio = page_folio(subpage);
> > > > > +		subpage = folio_page(folio, i);
> > > > > +		subfolio = page_folio(subpage);
> > > > 
> > > > No problems with the code, but I am not in love with the name subfolio.
> > > > I know it is patterned after 'subpage'.  For better or worse, the term
> > > > subpage is used throughout the kernel.  This would be the first usage of
> > > > the term 'subfolio'.
> > > > 
> > > > Matthew do you have any comments on the naming?  It is local to hugetlb,
> > > > but I would hate to see use of the term subfolio based on its introduction
> > > > here.
> > > 
> > > I'm really not a fan of it either.  I intended to dive into this patch
> > > and understand the function it's modifying, in the hopes of suggesting
> > > a better name and/or method.
> > 
> > At a high level, this routine is splitting a very large folio (1G for
> > example) into multiple large folios of a smaller size (512 2M folios for
> > example).  The loop is iterating through the very large folio at
> > increments of the smaller large folio.  subfolio (previously subpage) is
> > used to point to the smaller large folio within the loop.
> > 
> If folio does not need to be part of the variable name, how about something
> like 'demote_target'? The prep call inside the loop would then look like:
> 
> prep_new_hugetlb_folio(target_hstate, demote_target, nid);
> 
> so it is still clear that demote_target is a folio. A more concise version
> could also be 'demote_dst' but that seems more ambiguous than target.

I am OK with that naming.  Primary concern was the introduction of the
term subfolio.
-- 
Mike Kravetz