linux-ext4 - Re: [PATCH 25/31] ext4: Convert ext4_block_write

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Message-Id: <874jqm83kh.fsf@doe.com>
Date:   Wed, 15 Mar 2023 20:27:50 +0530
From:   Ritesh Harjani (IBM) <ritesh.list@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Theodore Tso <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 25/31] ext4: Convert ext4_block_write_begin() to take a folio

Matthew Wilcox <willy@...radead.org> writes:

> On Mon, Mar 06, 2023 at 08:51:45PM +0530, Ritesh Harjani wrote:
>> Matthew Wilcox <willy@...radead.org> writes:
>> 
>> > On Mon, Mar 06, 2023 at 12:21:48PM +0530, Ritesh Harjani wrote:
>> >> "Matthew Wilcox (Oracle)" <willy@...radead.org> writes:
>> >>
>> >> > All the callers now have a folio, so pass that in and operate on folios.
>> >> > Removes four calls to compound_head().
>> >>
>> >> Why do you say four? Isn't it 3 calls of PageUptodate(page) which
>> >> removes calls to compound_head()? Which one did I miss?
>> >>
>> >> > -	BUG_ON(!PageLocked(page));
>> >> > +	BUG_ON(!folio_test_locked(folio));
>> >
>> > That one ;-)
>> 
>> __PAGEFLAG(Locked, locked, PF_NO_TAIL)
>> 
>> #define __PAGEFLAG(uname, lname, policy)				\
>> 	TESTPAGEFLAG(uname, lname, policy)				\
>> 	__SETPAGEFLAG(uname, lname, policy)				\
>> 	__CLEARPAGEFLAG(uname, lname, policy)
>> 
>> #define TESTPAGEFLAG(uname, lname, policy)				\
>> static __always_inline bool folio_test_##lname(struct folio *folio)	\
>> { return test_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); }	\
>> static __always_inline int Page##uname(struct page *page)		\
>> { return test_bit(PG_##lname, &policy(page, 0)->flags); }
>> 
>> How? PageLocked(page) doesn't do any compount_head() calls no?
>
> You missed one piece of the definition ...
>
> #define PF_NO_TAIL(page, enforce) ({                                    \
>                 VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page);     \
>                 PF_POISONED_CHECK(compound_head(page)); })

aah yes, right. Thanks for pointing it.

-ritesh