linux-kernel - [PATCH v2 4/7] mm, swap: don't update the counter up-front

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Message-ID: <20250224180212.22802-5-ryncsn@gmail.com>
Date: Tue, 25 Feb 2025 02:02:09 +0800
From: Kairui Song <ryncsn@...il.com>
To: linux-mm@...ck.org
Cc: 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>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Kalesh Singh <kaleshsingh@...gle.com>,
	Matthew Wilcox <willy@...radead.org>,
	linux-kernel@...r.kernel.org,
	Kairui Song <kasong@...cent.com>
Subject: [PATCH v2 4/7] mm, swap: don't update the counter up-front

From: Kairui Song <kasong@...cent.com>

The counter update before allocation design was useful to avoid
unnecessary scan when device is full, so it will abort early if the
counter indicates the device is full. But that is an uncommon case,
and now scanning of a full device is very fast, so the up-front update
is not helpful any more.

Remove it and simplify the slot allocation logic.

Signed-off-by: Kairui Song <kasong@...cent.com>
---
 mm/swapfile.c | 18 ++----------------
 1 file changed, 2 insertions(+), 16 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6f2de59c6355..db836670c334 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1201,22 +1201,10 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
 	int order = swap_entry_order(entry_order);
 	unsigned long size = 1 << order;
 	struct swap_info_struct *si, *next;
-	long avail_pgs;
 	int n_ret = 0;
 	int node;
 
 	spin_lock(&swap_avail_lock);
-
-	avail_pgs = atomic_long_read(&nr_swap_pages) / size;
-	if (avail_pgs <= 0) {
-		spin_unlock(&swap_avail_lock);
-		goto noswap;
-	}
-
-	n_goal = min3((long)n_goal, (long)SWAP_BATCH, avail_pgs);
-
-	atomic_long_sub(n_goal * size, &nr_swap_pages);
-
 start_over:
 	node = numa_node_id();
 	plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
@@ -1250,10 +1238,8 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
 	spin_unlock(&swap_avail_lock);
 
 check_out:
-	if (n_ret < n_goal)
-		atomic_long_add((long)(n_goal - n_ret) * size,
-				&nr_swap_pages);
-noswap:
+	atomic_long_sub(n_ret * size, &nr_swap_pages);
+
 	return n_ret;
 }
 
-- 
2.48.1