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

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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?