linux-kernel - [PATCH] mm/madvise: fix WILLNEED on SHM/ANON to actually do something

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Date:	Fri, 23 May 2014 14:12:15 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	David Rientjes <rientjes@...gle.com>,
	Vladimir Cernov <gg.kaspersky@...il.com>, linux-mm@...ck.org,
	David Herrmann <dh.herrmann@...il.com>
Subject: [PATCH] mm/madvise: fix WILLNEED on SHM/ANON to actually do something

Currently, madvise(MADV_WILLNEED) on shmem with swap enabled is a no-op.
Problem is, we use find_get_page() to lookup shmem pages in the given
range. However, what we're actually interested in is swapped-out pages.
Therefore, our current code is a no-op:
    page = find_get_page(mapping, index);
    if (!radix_tree_exceptional_entry(page))
        bail-out;

find_get_page() never returns exceptional entries. Fix this by using
find_get_entry(). This was probably meant to be used right from the
beginning.

Signed-off-by: David Herrmann <dh.herrmann@...il.com>
---
 mm/madvise.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 539eeb9..a402f8f 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -195,7 +195,7 @@ static void force_shm_swapin_readahead(struct vm_area_struct *vma,
 	for (; start < end; start += PAGE_SIZE) {
 		index = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 
-		page = find_get_page(mapping, index);
+		page = find_get_entry(mapping, index);
 		if (!radix_tree_exceptional_entry(page)) {
 			if (page)
 				page_cache_release(page);
-- 
1.9.3

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