linux-kernel - [PATCH v3 2/2] mm/swap: remove swap_cache

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Message-ID: <20220625093346.48894-3-linmiaohe@huawei.com>
Date:   Sat, 25 Jun 2022 17:33:46 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <david@...hat.com>, <ying.huang@...el.com>,
        <songmuchun@...edance.com>, <quic_qiancai@...cinc.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH v3 2/2] mm/swap: remove swap_cache_info statistics

swap_cache_info are not statistics that could be easily used to tune system
performance because they are not easily accessile. Also they can't provide
really useful info when OOM occurs. Remove these statistics can also help
mitigate unneeded global swap_cache_info cacheline contention.

Suggested-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
Reviewed-by: David Hildenbrand <david@...hat.com>
Acked-by: "Huang, Ying" <ying.huang@...el.com>
Reviewed-by: Muchun Song <songmuchun@...edance.com>
---
 mm/swap_state.c | 17 -----------------
 1 file changed, 17 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index dd142624172b..e166051566f4 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -59,24 +59,11 @@ static bool enable_vma_readahead __read_mostly = true;
 #define GET_SWAP_RA_VAL(vma)					\
 	(atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
 
-#define INC_CACHE_INFO(x)	data_race(swap_cache_info.x++)
-#define ADD_CACHE_INFO(x, nr)	data_race(swap_cache_info.x += (nr))
-
-static struct {
-	unsigned long add_total;
-	unsigned long del_total;
-	unsigned long find_success;
-	unsigned long find_total;
-} swap_cache_info;
-
 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
 
 void show_swap_cache_info(void)
 {
 	printk("%lu pages in swap cache\n", total_swapcache_pages());
-	printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
-		swap_cache_info.add_total, swap_cache_info.del_total,
-		swap_cache_info.find_success, swap_cache_info.find_total);
 	printk("Free swap  = %ldkB\n",
 		get_nr_swap_pages() << (PAGE_SHIFT - 10));
 	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
@@ -133,7 +120,6 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry,
 		address_space->nrpages += nr;
 		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
 		__mod_lruvec_page_state(page, NR_SWAPCACHE, nr);
-		ADD_CACHE_INFO(add_total, nr);
 unlock:
 		xas_unlock_irq(&xas);
 	} while (xas_nomem(&xas, gfp));
@@ -173,7 +159,6 @@ void __delete_from_swap_cache(struct folio *folio,
 	address_space->nrpages -= nr;
 	__node_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
 	__lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr);
-	ADD_CACHE_INFO(del_total, nr);
 }
 
 /**
@@ -349,12 +334,10 @@ struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
 	page = find_get_page(swap_address_space(entry), swp_offset(entry));
 	put_swap_device(si);
 
-	INC_CACHE_INFO(find_total);
 	if (page) {
 		bool vma_ra = swap_use_vma_readahead();
 		bool readahead;
 
-		INC_CACHE_INFO(find_success);
 		/*
 		 * At the moment, we don't support PG_readahead for anon THP
 		 * so let's bail out rather than confusing the readahead stat.
-- 
2.23.0