linux-kernel - [PATCH 1/4] mm: swapoff: shmem_find_swap

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Date:   Mon, 8 Apr 2019 12:56:12 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>,
        Vineeth Pillai <vpillai@...italocean.com>,
        Kelley Nielsen <kelleynnn@...il.com>,
        Rik van Riel <riel@...riel.com>,
        Huang Ying <ying.huang@...el.com>,
        Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: [PATCH 1/4] mm: swapoff: shmem_find_swap_entries() filter out other
 types

Swapfile "type" was passed all the way down to shmem_unuse_inode(), but
then forgotten from shmem_find_swap_entries(): with the result that
removing one swapfile would try to free up all the swap from shmem - no
problem when only one swapfile anyway, but counter-productive when more,
causing swapoff to be unnecessarily OOM-killed when it should succeed.

Fixes: b56a2d8af914 ("mm: rid swapoff of quadratic complexity")
Signed-off-by: Hugh Dickins <hughd@...gle.com>
---

 mm/shmem.c |   18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

--- 5.1-rc4/mm/shmem.c	2019-03-17 16:18:15.701823872 -0700
+++ linux/mm/shmem.c	2019-04-07 19:12:23.603858531 -0700
@@ -1099,10 +1099,11 @@ extern struct swap_info_struct *swap_inf
 static int shmem_find_swap_entries(struct address_space *mapping,
 				   pgoff_t start, unsigned int nr_entries,
 				   struct page **entries, pgoff_t *indices,
-				   bool frontswap)
+				   unsigned int type, bool frontswap)
 {
 	XA_STATE(xas, &mapping->i_pages, start);
 	struct page *page;
+	swp_entry_t entry;
 	unsigned int ret = 0;
 
 	if (!nr_entries)
@@ -1116,13 +1117,12 @@ static int shmem_find_swap_entries(struc
 		if (!xa_is_value(page))
 			continue;
 
-		if (frontswap) {
-			swp_entry_t entry = radix_to_swp_entry(page);
-
-			if (!frontswap_test(swap_info[swp_type(entry)],
-					    swp_offset(entry)))
-				continue;
-		}
+		entry = radix_to_swp_entry(page);
+		if (swp_type(entry) != type)
+			continue;
+		if (frontswap &&
+		    !frontswap_test(swap_info[type], swp_offset(entry)))
+			continue;
 
 		indices[ret] = xas.xa_index;
 		entries[ret] = page;
@@ -1194,7 +1194,7 @@ static int shmem_unuse_inode(struct inod
 
 		pvec.nr = shmem_find_swap_entries(mapping, start, nr_entries,
 						  pvec.pages, indices,
-						  frontswap);
+						  type, frontswap);
 		if (pvec.nr == 0) {
 			ret = 0;
 			break;