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From: SeongJae Park <sj@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	SeongJae Park <sj@kernel.org>,
	damon@lists.linux.dev, linux-mm@kvack.org,
	vishal.moola@gmail.com, david@redhat.com
Subject: Re: [PATCH -next v3 2/7] mm/damon: introduce damon_get_folio()
Date: Wed, 28 Dec 2022 23:14:17 +0000	[thread overview]
Message-ID: <20221228231417.150148-1-sj@kernel.org> (raw)
In-Reply-To: <Y6zE5DsGU1CRpWS2@casper.infradead.org>

Hi Matthew,

On Wed, 28 Dec 2022 22:36:20 +0000 Matthew Wilcox <willy@infradead.org> wrote:

> On Wed, Dec 28, 2022 at 07:34:08PM +0800, Kefeng Wang wrote:
> > +static inline struct page *damon_get_page(unsigned long pfn)
> > +{
> > +	struct folio *folio = damon_get_folio(pfn);
> > +
> > +	/* when folio is NULL, return &(0->page) mean return NULL */
> > +	return &folio->page;
> I really don't think this comment is needed.  This is the standard idiom
> for converting from a folio to its head page.

Well, I think some of DAMON code readers (at least me) might not yet that
familiar with Folio, as it has not been a while since DAMON started using
Folio.  Also, maybe I overlooked some comments or documents, but I was unable
to sure if the offset of 'page' in 'folio' is intended to be never changed with
any future changes, or not.  So I thought adding one more line of explanation
here could be helpful for someone.

I also show some code using 'folio_page(folio, 0)', so I might not be the only
one who at least sometimes forget the idiom.  For helping people remember this
idiom easier, what do you think about having a new macro or static inline
function, say, 'folio_head_page()' and comment why passing NULL is ok on the
function?  IMHO, that would be easier to read.


  reply	other threads:[~2022-12-28 23:14 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-28 11:34 [PATCH -next v3 0/7] mm: convert page_idle/damon to use folios Kefeng Wang
2022-12-28 11:34 ` [PATCH -next v3 1/7] mm: page_idle: convert page idle " Kefeng Wang
2022-12-28 17:46   ` SeongJae Park
2022-12-28 11:34 ` [PATCH -next v3 2/7] mm/damon: introduce damon_get_folio() Kefeng Wang
2022-12-28 22:36   ` Matthew Wilcox
2022-12-28 23:14     ` SeongJae Park [this message]
2022-12-28 11:34 ` [PATCH -next v3 3/7] mm/damon: convert damon_ptep/pmdp_mkold() to use folios Kefeng Wang
2022-12-28 11:34 ` [PATCH -next v3 4/7] mm/damon/paddr: convert damon_pa_*() " Kefeng Wang
2022-12-29 20:36   ` Matthew Wilcox
2022-12-30  6:40     ` Kefeng Wang
2022-12-28 11:34 ` [PATCH -next v3 5/7] mm/damon/vaddr: convert damon_young_pmd_entry() to use folio Kefeng Wang
2022-12-29 21:06   ` Matthew Wilcox
2022-12-29 21:31     ` SeongJae Park
2022-12-28 11:34 ` [PATCH -next v3 6/7] mm/damon: remove unneed damon_get_page() Kefeng Wang
2022-12-28 17:49   ` SeongJae Park
2022-12-28 11:34 ` [PATCH -next v3 7/7] mm/damon/vaddr: convert hugetlb related function to use folios Kefeng Wang
2022-12-28 17:51   ` SeongJae Park
2022-12-28 17:55 ` [PATCH -next v3 0/7] mm: convert page_idle/damon " SeongJae Park
2022-12-29  2:16   ` Kefeng Wang

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