linux-ext4 - Re: [RESEND PATCH v10 25/25] dept: Track the potential waits of PG

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Message-ID: <ZOLnRSdH4Wcrl67L@casper.infradead.org>
Date:   Mon, 21 Aug 2023 05:25:41 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Byungchul Park <byungchul@...com>
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Subject: Re: [RESEND PATCH v10 25/25] dept: Track the potential waits of
 PG_{locked,writeback}

On Mon, Aug 21, 2023 at 12:46:37PM +0900, Byungchul Park wrote:
> @@ -377,44 +421,88 @@ static __always_inline int Page##uname(struct page *page)		\
>  #define SETPAGEFLAG(uname, lname, policy)				\
>  static __always_inline							\
>  void folio_set_##lname(struct folio *folio)				\
> -{ set_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); }		\
> +{									\
> +	set_bit(PG_##lname, folio_flags(folio, FOLIO_##policy));	\
> +	dept_page_set_bit(&folio->page, PG_##lname);			\

The PG_locked and PG_writeback bits only actually exist in the folio;
the ones in struct page are just legacy and never actually used.
Perhaps we could make the APIs more folio-based and less page-based?

>  static __always_inline void SetPage##uname(struct page *page)		\
> -{ set_bit(PG_##lname, &policy(page, 1)->flags); }
> +{									\
> +	set_bit(PG_##lname, &policy(page, 1)->flags);			\
> +	dept_page_set_bit(page, PG_##lname);				\
> +}

I don't think we ever call this for PG_writeback or PG_locked.  If
I'm wrong, we can probably fix that ;-)

>  static __always_inline void __SetPage##uname(struct page *page)		\
> -{ __set_bit(PG_##lname, &policy(page, 1)->flags); }
> +{									\
> +	__set_bit(PG_##lname, &policy(page, 1)->flags);			\
> +	dept_page_set_bit(page, PG_##lname);				\
> +}

Umm.  We do call __SetPageLocked() though ... I'll fix those up to
be __set_folio_locked().