From: Baoquan He <bhe@redhat.com>
To: Kairui Song <ryncsn@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, chrisl@kernel.org
Subject: Re: [PATCH 04/12] mm/swap: skip scanning cluster range if it's empty cluster
Date: Thu, 6 Feb 2025 09:40:57 +0800 [thread overview]
Message-ID: <Z6QTKQPKXDEpWWKb@fedora> (raw)
In-Reply-To: <CAMgjq7CYC4xfAkp9Y7g=3rw=iqTj_pQAjrnwDC1orkdUhnOCSQ@mail.gmail.com>
On 02/06/25 at 01:07am, Kairui Song wrote:
> On Wed, Feb 5, 2025 at 5:27 PM Baoquan He <bhe@redhat.com> wrote:
> >
> > Since ci->lock has been taken when isolating cluster from
> > si->free_clusters or taking si->percpu_cluster->next[order],
> > it's unnecessary to scan and check the cluster range availability
> > if i'ts empty cluster, and this can accelerate the huge page
> > swapping.
> >
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> > mm/swapfile.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 9c9a4ec6d4c6..61efde853eea 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -729,6 +729,9 @@ static bool cluster_scan_range(struct swap_info_struct *si,
> > unsigned long offset, end = start + nr_pages;
> > unsigned char *map = si->swap_map;
> >
> > + if (cluster_is_empty(ci))
> > + return true;
> > +
>
> Hi Baoquan,
>
> Thanks for the series.
Thanks for your reviewing.
>
> Most commits are looking great, but this one is a bit questionable.
> cluster_scan_range is only called by alloc_swap_scan_cluster, and it
> already checks if the cluster has enough empty slots to use, so this
> might be redundant.
Hmm, maybe no. Assume we want to allocate 2M space on system with 4K
page size. Even if a empty cluster is taken into consideration,
cluster_scan_range() will loop 512 times to check if each slot is
available. That for sure is not necessary in the case, while the added
empty cluster checking is very cheap.
>
> It is possible that cluster_scan_range sees an empty cluster if the
> cluster lock was dropped for reclaiming HAS_CACHE, but the chance
> should be extremely low, that this might be a negative optimization.
It may be not like that. If it's empty cluster, the added checking will
return directly. Then 'need_reclaim' is kept false, there's no chance to
drop cluster lock to do reclaiming for HAS_CACHE. Means for empty
cluster scanning, the ci->lock is kept held. Not sure if I missed
anything.
Thanks
Baoquan
next prev parent reply other threads:[~2025-02-06 1:41 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-05 9:27 [PATCH 00/12] Tiny cleanup and improvements about SWAP code Baoquan He
2025-02-05 9:27 ` [PATCH 01/12] mm/swap_state.c: fix the obsolete code comment Baoquan He
2025-02-05 9:27 ` [PATCH 02/12] mm/swap_state.c: optimize the code in clear_shadow_from_swap_cache() Baoquan He
2025-02-05 9:27 ` [PATCH 03/12] mm/swap: remove SWAP_FLAG_PRIO_SHIFT Baoquan He
2025-02-05 9:27 ` [PATCH 04/12] mm/swap: skip scanning cluster range if it's empty cluster Baoquan He
2025-02-05 17:07 ` Kairui Song
2025-02-06 1:40 ` Baoquan He [this message]
2025-02-06 2:14 ` Kairui Song
2025-02-05 9:27 ` [PATCH 05/12] mm/swap: rename swap_is_has_cache() to swap_only_has_cache() Baoquan He
2025-02-05 9:27 ` [PATCH 06/12] mm/swapfile.c: update the code comment above swap_count_continued() Baoquan He
2025-02-06 7:50 ` Kairui Song
2025-02-07 2:46 ` Baoquan He
2025-02-07 2:50 ` [PATCH v2 " Baoquan He
2025-02-05 9:27 ` [PATCH 07/12] mm/swapfile.c: optimize code in setup_clusters() Baoquan He
2025-02-05 9:27 ` [PATCH 08/12] mm/swap_state.c: remove the meaningless code comment Baoquan He
2025-02-05 9:27 ` [PATCH 09/12] mm/swapfile.c: remove the unneeded checking Baoquan He
2025-02-05 9:27 ` [PATCH 10/12] mm/swap: rename swap_swapcount() to swap_entry_swapped() Baoquan He
2025-02-05 9:27 ` [PATCH 11/12] mm/swapfile.c: remove the incorrect code comment Baoquan He
2025-02-05 9:27 ` [PATCH 12/12] mm/swapfile.c: open code cluster_alloc_swap() Baoquan He
2025-02-07 9:36 ` [PATCH 00/12] Tiny cleanup and improvements about SWAP code Kairui Song
2025-02-08 1:08 ` Baoquan He
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