linux-kernel - Re: [v5 4/7] mm: Separate move/undo doing on folio list from migrate_pages

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Message-ID: <20240115084825.GA18164@system.software.com>
Date: Mon, 15 Jan 2024 17:48:25 +0900
From: Byungchul Park <byungchul@...com>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernel_team@...ynix.com, akpm@...ux-foundation.org,
	ying.huang@...el.com, namit@...are.com, xhao@...ux.alibaba.com,
	mgorman@...hsingularity.net, hughd@...gle.com, david@...hat.com,
	peterz@...radead.org, luto@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com
Subject: Re: [v5 4/7] mm: Separate move/undo doing on folio list from
 migrate_pages_batch()

On Mon, Jan 15, 2024 at 11:08:18AM +0900, Byungchul Park wrote:
> On Thu, Jan 11, 2024 at 03:42:55PM +0000, Matthew Wilcox wrote:
> > On Thu, Jan 11, 2024 at 03:07:54PM +0900, Byungchul Park wrote:
> > > +static void migrate_folios_move(struct list_head *src_folios,
> > > +		struct list_head *dst_folios,
> > > +		free_folio_t put_new_folio, unsigned long private,
> > > +		enum migrate_mode mode, int reason,
> > > +		struct list_head *ret_folios,
> > > +		struct migrate_pages_stats *stats,
> > > +		int *retry, int *thp_retry, int *nr_failed,
> > > +		int *nr_retry_pages)
> > > +{
> > > +	struct folio *folio, *folio2, *dst, *dst2;
> > > +	bool is_thp;
> > > +	int nr_pages;
> > > +	int rc;
> > > +
> > > +	dst = list_first_entry(dst_folios, struct folio, lru);
> > > +	dst2 = list_next_entry(dst, lru);
> > > +	list_for_each_entry_safe(folio, folio2, src_folios, lru) {
> > > +		is_thp = folio_test_large(folio) && folio_test_pmd_mappable(folio);

JFYI, in the v4 patch set, I hadn't changed the original code that I
refactored. I just copied and pasted this part from the original code.

> > 
> > You don't need to call folio_test_large() first.  folio_order() includes
> > a call to test_large() so it can return 0.
> > 
> > > +		nr_pages = folio_nr_pages(folio);
> > 
> > ... or since you're calculating this anyway,
> > 
> > 		is_thp = nr_pages >= HPAGE_PMD_NR

I didn't apply what you suggested me here to the next version yet
because I was not sure if it'd make the code more readable.

Thanks anyway!

	Byungchul

> Cool. Thanks.
> 
> 	Byungchul
> 
> > perhaps