linux-kernel - Re: [PATCH 7/7] mm, swap: simplify folio swap allocation

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Message-ID: <Z6-j924RCEBuDFHO@casper.infradead.org>
Date: Fri, 14 Feb 2025 20:13:43 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Kairui Song <kasong@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Chris Li <chrisl@...nel.org>, Barry Song <v-songbaohua@...o.com>,
	Hugh Dickins <hughd@...gle.com>,
	Yosry Ahmed <yosryahmed@...gle.com>,
	"Huang, Ying" <ying.huang@...ux.alibaba.com>,
	Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Kalesh Singh <kaleshsingh@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] mm, swap: simplify folio swap allocation

On Sat, Feb 15, 2025 at 01:57:09AM +0800, Kairui Song wrote:
> @@ -1648,20 +1639,20 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
>  	if (list_empty(&info->swaplist))
>  		list_add(&info->swaplist, &shmem_swaplist);
>  
> -	if (add_to_swap_cache(folio, swap,
> -			__GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN,
> -			NULL) == 0) {
> +	if (folio_alloc_swap(folio, __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN)) {

add_to_swap_cache() returns 0 on success or -errno.

folio_alloc_swap returns true on success.

That would seem to indicate you should change the polarity of this test?

Or should folio_alloc_swap() return an errno?  Is there value in
distinguishing why we couldn't alloc swap (ENOMEM vs ENOSPC, perhaps?)