[patch 049/200] mm/swap_state: skip meaningless swap cache readahead when ra_info.win == 0

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From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Subject: mm/swap_state: skip meaningless swap cache readahead when ra_info.win == 0

swap_ra_info() may leave ra_info untouched in non_swap_entry() case as
page table lock is not held.  In this case, we have ra_info.nr_pte == 0
and it is meaningless to continue with swap cache readahead.  Skip such
ops by init ra_info.win = 1.

[akpm@xxxxxxxxxxxxxxxxxxxx: clean up struct init]
Link: https://lkml.kernel.org/r/20201009133059.58407-1-linmiaohe@xxxxxxxxxx
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/swap_state.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/swap_state.c~mm-swap_state-skip-meaningless-swap-cache-readahead-when-ra_infowin-==-0
+++ a/mm/swap_state.c
@@ -839,7 +839,9 @@ static struct page *swap_vma_readahead(s
 	swp_entry_t entry;
 	unsigned int i;
 	bool page_allocated;
-	struct vma_swap_readahead ra_info = {0,};
+	struct vma_swap_readahead ra_info = {
+		.win = 1,
+	};
 
 	swap_ra_info(vmf, &ra_info);
 	if (ra_info.win == 1)
_




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