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Message-ID: <CAMgjq7CL1pUr25efhu+bT1PRdqw+TkAaCCsBi-1DRBfd28N4OQ@mail.gmail.com>
Date: Wed, 13 Aug 2025 00:56:35 +0800
From: Kairui Song <ryncsn@...il.com>
To: Chris Li <chrisl@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Kemeng Shi <shikemeng@...weicloud.com>,
Nhat Pham <nphamcs@...il.com>, Baoquan He <bhe@...hat.com>, Barry Song <baohua@...nel.org>,
"Huang, Ying" <ying.huang@...ux.alibaba.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] mm/swapfile.c: introduce function alloc_swap_scan_list()
On Tue, Aug 12, 2025 at 5:13 PM Chris Li <chrisl@...nel.org> wrote:
>
> alloc_swap_scan_list() will scan the whole list or the first cluster.
>
> This reduces the repeat patterns of isolating a cluster then scanning that
> cluster. As a result, cluster_alloc_swap_entry() is shorter and shallower.
>
> No functional change.
>
> Signed-off-by: Chris Li <chrisl@...nel.org>
> ---
> mm/swapfile.c | 86 ++++++++++++++++++++++++++++++++---------------------------
> 1 file changed, 47 insertions(+), 39 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 4a0cf4fb348d..a7ffabbe65ef 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -820,6 +820,29 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si,
> return found;
> }
>
> +static unsigned int alloc_swap_scan_list(struct swap_info_struct *si,
> + struct list_head *list,
> + unsigned int order,
> + unsigned char usage,
> + bool scan_all)
> +{
> + unsigned int found = SWAP_ENTRY_INVALID;
> +
> + do {
> + struct swap_cluster_info *ci = isolate_lock_cluster(si, list);
> + unsigned long offset;
> +
> + if (!ci)
> + break;
> + offset = cluster_offset(si, ci);
> + found = alloc_swap_scan_cluster(si, ci, offset, order, usage);
> + if (found)
> + break;
> + } while (scan_all);
> +
> + return found;
> +}
> +
> static void swap_reclaim_full_clusters(struct swap_info_struct *si, bool force)
> {
> long to_scan = 1;
> @@ -913,32 +936,24 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
> * to spread out the writes.
> */
> if (si->flags & SWP_PAGE_DISCARD) {
> - ci = isolate_lock_cluster(si, &si->free_clusters);
> - if (ci) {
> - found = alloc_swap_scan_cluster(si, ci, cluster_offset(si, ci),
> - order, usage);
> - if (found)
> - goto done;
> - }
> + found = alloc_swap_scan_list(si, &si->free_clusters, order, usage,
> + false);
> + if (found)
> + goto done;
> }
>
> if (order < PMD_ORDER) {
> - while ((ci = isolate_lock_cluster(si, &si->nonfull_clusters[order]))) {
> - found = alloc_swap_scan_cluster(si, ci, cluster_offset(si, ci),
> - order, usage);
> - if (found)
> - goto done;
> - }
> + found = alloc_swap_scan_list(si, &si->nonfull_clusters[order],
> + order, usage, true);
> + if (found)
> + goto done;
> }
>
> if (!(si->flags & SWP_PAGE_DISCARD)) {
> - ci = isolate_lock_cluster(si, &si->free_clusters);
> - if (ci) {
> - found = alloc_swap_scan_cluster(si, ci, cluster_offset(si, ci),
> - order, usage);
> - if (found)
> - goto done;
> - }
> + found = alloc_swap_scan_list(si, &si->free_clusters, order, usage,
> + false);
> + if (found)
> + goto done;
> }
>
> /* Try reclaim full clusters if free and nonfull lists are drained */
> @@ -952,13 +967,10 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
> * failure is not critical. Scanning one cluster still
> * keeps the list rotated and reclaimed (for HAS_CACHE).
> */
> - ci = isolate_lock_cluster(si, &si->frag_clusters[order]);
> - if (ci) {
> - found = alloc_swap_scan_cluster(si, ci, cluster_offset(si, ci),
> - order, usage);
> - if (found)
> - goto done;
> - }
> + found = alloc_swap_scan_list(si, &si->frag_clusters[order], order,
> + usage, false);
> + if (found)
> + goto done;
> }
>
> /*
> @@ -977,19 +989,15 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
> * Clusters here have at least one usable slots and can't fail order 0
> * allocation, but reclaim may drop si->lock and race with another user.
> */
> - while ((ci = isolate_lock_cluster(si, &si->frag_clusters[o]))) {
> - found = alloc_swap_scan_cluster(si, ci, cluster_offset(si, ci),
> - 0, usage);
> - if (found)
> - goto done;
> - }
> + found = alloc_swap_scan_list(si, &si->frag_clusters[o],
> + 0, usage, true);
> + if (found)
> + goto done;
>
> - while ((ci = isolate_lock_cluster(si, &si->nonfull_clusters[o]))) {
> - found = alloc_swap_scan_cluster(si, ci, cluster_offset(si, ci),
> - 0, usage);
> - if (found)
> - goto done;
> - }
> + found = alloc_swap_scan_list(si, &si->nonfull_clusters[o],
> + 0, usage, true);
> + if (found)
> + goto done;
> }
> done:
> if (!(si->flags & SWP_SOLIDSTATE))
>
> --
> 2.43.0
>
I've been testing on top of a locally updated version of V2 for about
two days, and it's identical to this one. This looks great, thanks!
Reviewed-by: Kairui Song <kasong@...cent.com>
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