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From:   Kairui Song <ryncsn@gmail.com>
To:     linux-mm@kvack.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        "Huang, Ying" <ying.huang@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@suse.com>, linux-kernel@vger.kernel.org,
        Kairui Song <kasong@tencent.com>
Subject: [PATCH 04/24] mm/swap: avoid setting page lock bit and doing extra unlock check
Date:   Mon, 20 Nov 2023 03:47:20 +0800
Message-ID: <20231119194740.94101-5-ryncsn@gmail.com>
In-Reply-To: <20231119194740.94101-1-ryncsn@gmail.com>
References: <20231119194740.94101-1-ryncsn@gmail.com>
Reply-To: Kairui Song <kasong@tencent.com>
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From: Kairui Song <kasong@tencent.com>

When swapping in a page, mem_cgroup_swapin_charge_folio is called for new
allocated folio, nothing else is referencing the folio so no need to set
the lock bit. This avoided doing unlock check on error path.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 mm/swap_state.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index ac4fa404eaa7..45dd8b7c195d 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -458,6 +458,8 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 						mpol, ilx, numa_node_id());
 		if (!folio)
                         goto fail_put_swap;
+		if (mem_cgroup_swapin_charge_folio(folio, NULL, gfp_mask, entry))
+			goto fail_put_folio;
 
 		/*
 		 * Swap entry may have been freed since our caller observed it.
@@ -483,13 +485,9 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 	/*
 	 * The swap entry is ours to swap in. Prepare the new page.
 	 */
-
 	__folio_set_locked(folio);
 	__folio_set_swapbacked(folio);
 
-	if (mem_cgroup_swapin_charge_folio(folio, NULL, gfp_mask, entry))
-		goto fail_unlock;
-
 	/* May fail (-ENOMEM) if XArray node allocation failed. */
 	if (add_to_swap_cache(folio, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow))
 		goto fail_unlock;
@@ -510,6 +508,7 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 fail_unlock:
 	put_swap_folio(folio, entry);
 	folio_unlock(folio);
+fail_put_folio:
 	folio_put(folio);
 fail_put_swap:
 	put_swap_device(si);
@@ -873,16 +872,15 @@ struct page *swapin_no_readahead(swp_entry_t entry, gfp_t gfp_mask,
 	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0,
 				vma, vmf->address, false);
 	if (folio) {
-		__folio_set_locked(folio);
-		__folio_set_swapbacked(folio);
-
-		if (mem_cgroup_swapin_charge_folio(folio,
-					vma->vm_mm, GFP_KERNEL,
-					entry)) {
-			folio_unlock(folio);
+		if (mem_cgroup_swapin_charge_folio(folio, vma->vm_mm,
+						   GFP_KERNEL, entry)) {
 			folio_put(folio);
 			return NULL;
 		}
+
+		__folio_set_locked(folio);
+		__folio_set_swapbacked(folio);
+
 		mem_cgroup_swapin_uncharge_swap(entry);
 
 		shadow = get_shadow_from_swap_cache(entry);
-- 
2.42.0