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Date:   Mon, 30 Oct 2023 23:22:18 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Gregory Price <gourry.memverge@gmail.com>
Cc:     linux-mm@kvack.org, akpm@linux-foundation.org, david@redhat.com,
        vbabka@suse.cz, naoya.horiguchi@linux.dev,
        linux-kernel@vger.kernel.org,
        Gregory Price <gregory.price@memverge.com>
Subject: Re: [PATCH v2] kpageflags: respect folio head-page flag placement
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On Mon, Oct 30, 2023 at 02:00:05PM -0400, Gregory Price wrote:
> kpageflags reads page-flags directly from the page, even when the
> respective flag is only updated on the headpage of a folio.
> 
> Update bitchecks to use PAGEFLAG() interfaces to check folio for the
> referenced, dirty, lru, active, and unevictable bits.

But uptodate, writeback and reclaim (amongst others) are also defined
only on the head page.

>  	u |= kpf_copy_bit(k, KPF_UPTODATE,	PG_uptodate);
>  	u |= kpf_copy_bit(k, KPF_WRITEBACK,	PG_writeback);
>  
>  	u |= kpf_copy_bit(k, KPF_RECLAIM,	PG_reclaim);
>  
>  	if (PageSwapCache(page))
>  		u |= 1 << KPF_SWAPCACHE;
>  	u |= kpf_copy_bit(k, KPF_SWAPBACKED,	PG_swapbacked);
>  
>  	u |= kpf_copy_bit(k, KPF_MLOCKED,	PG_mlocked);