linux-kernel - [PATCH] mm: refactor si_mem

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Message-ID: <20230827110848.43510-1-lstoakes@gmail.com>
Date:   Sun, 27 Aug 2023 12:08:48 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Lorenzo Stoakes <lstoakes@...il.com>
Subject: [PATCH] mm: refactor si_mem_available()

The si_mem_available() function needlessly places LRU statistics into an
array before retrieving only two of them, simply access those directly.

In addition, refactor the code so that the blocks of code which calculate
the page cache and reclaimable components each resemble one another to
clearly indicate we cap both against wmark_low in the same fashion.

Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
---
 mm/show_mem.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/mm/show_mem.c b/mm/show_mem.c
index 4b888b18bdde..ba0808d6917f 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -34,13 +34,8 @@ long si_mem_available(void)
 	long available;
 	unsigned long pagecache;
 	unsigned long wmark_low = 0;
-	unsigned long pages[NR_LRU_LISTS];
 	unsigned long reclaimable;
 	struct zone *zone;
-	int lru;
-
-	for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
-		pages[lru] = global_node_page_state(NR_LRU_BASE + lru);
 
 	for_each_zone(zone)
 		wmark_low += low_wmark_pages(zone);
@@ -56,7 +51,8 @@ long si_mem_available(void)
 	 * start swapping or thrashing. Assume at least half of the page
 	 * cache, or the low watermark worth of cache, needs to stay.
 	 */
-	pagecache = pages[LRU_ACTIVE_FILE] + pages[LRU_INACTIVE_FILE];
+	pagecache = global_node_page_state(NR_ACTIVE_FILE) +
+		global_node_page_state(NR_INACTIVE_FILE);
 	pagecache -= min(pagecache / 2, wmark_low);
 	available += pagecache;
 
@@ -67,7 +63,8 @@ long si_mem_available(void)
 	 */
 	reclaimable = global_node_page_state_pages(NR_SLAB_RECLAIMABLE_B) +
 		global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE);
-	available += reclaimable - min(reclaimable / 2, wmark_low);
+	reclaimable -= min(reclaimable / 2, wmark_low);
+	available += reclaimable;
 
 	if (available < 0)
 		available = 0;
-- 
2.42.0