linux-kernel - Re: [PATCH net-next 04/12] mm: Make the page_frag

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Message-ID: <20230526175002.2591ccae@kernel.org>
Date:   Fri, 26 May 2023 17:50:02 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Jeroen de Borst <jeroendb@...gle.com>,
        Catherine Sullivan <csully@...gle.com>,
        Shailend Chand <shailend@...gle.com>,
        Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-nvme@...ts.infradead.org
Subject: Re: [PATCH net-next 04/12] mm: Make the page_frag_cache allocator
 use multipage folios

On Wed, 24 May 2023 16:33:03 +0100 David Howells wrote:
> -	offset = nc->offset - fragsz;
> -	if (unlikely(offset < 0)) {
> -		page = virt_to_page(nc->va);
> -
> -		if (page_ref_count(page) != nc->pagecnt_bias)
> +	offset = nc->offset;
> +	if (unlikely(fragsz > offset)) {
> +		/* Reuse the folio if everyone we gave it to has finished with
> +		 * it.
> +		 */
> +		if (!folio_ref_sub_and_test(folio, nc->pagecnt_bias)) {
> +			nc->folio = NULL;
>  			goto refill;
> +		}
> +
>  		if (unlikely(nc->pfmemalloc)) {
> -			page_ref_sub(page, nc->pagecnt_bias - 1);
> -			__free_pages(page, compound_order(page));
> +			__folio_put(folio);

This is not a pure 1:1 page -> folio conversion.
Why mix conversion with other code changes?