linux-kernel - Re: [PATCH] block: Remove special-casing of compound pages

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Message-ID: <ZXJCxbAm1_V7lPnF@kbusch-mbp>
Date:   Thu, 7 Dec 2023 15:10:13 -0700
From:   Keith Busch <kbusch@...nel.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] block: Remove special-casing of compound pages

On Mon, Aug 14, 2023 at 03:41:00PM +0100, Matthew Wilcox (Oracle) wrote:
>  void __bio_release_pages(struct bio *bio, bool mark_dirty)
>  {
> -	struct bvec_iter_all iter_all;
> -	struct bio_vec *bvec;
> +	struct folio_iter fi;
> +
> +	bio_for_each_folio_all(fi, bio) {
> +		struct page *page;
> +		size_t done = 0;
>  
> -	bio_for_each_segment_all(bvec, bio, iter_all) {
> -		if (mark_dirty && !PageCompound(bvec->bv_page))
> -			set_page_dirty_lock(bvec->bv_page);
> -		bio_release_page(bio, bvec->bv_page);
> +		if (mark_dirty) {
> +			folio_lock(fi.folio);
> +			folio_mark_dirty(fi.folio);
> +			folio_unlock(fi.folio);
> +		}
> +		page = folio_page(fi.folio, fi.offset / PAGE_SIZE);
> +		do {
> +			bio_release_page(bio, page++);
> +			done += PAGE_SIZE;
> +		} while (done < fi.length);
>  	}
>  }

Is it okay to release same-folio pages while creating the bio instead of
releasing all the pages at the completion? If so, the completion could
provide just the final bio_release_page() instead looping. I'm more
confirming if that's an appropriate way to use folios here.