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

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Message-ID: <CAMgjq7CRU8gkbC-ehjyMOZmS=bkXiKFKa1YUdgwLUdPXXJuVYg@mail.gmail.com>
Date: Sat, 15 Feb 2025 14:40:34 +0800
From: Kairui Song <ryncsn@...il.com>
To: Matthew Wilcox <willy@...radead.org>
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 4:13 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> 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?

I think I already did? It was (add_to_swap_cache(...) == 0), now it's
(folio_alloc_swap(...))

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

Good idea, return an error value might be more helpful in the future,
will update this part.