2023-10-17 01:18:53

by Kairui Song

Subject: [PATCH] mm/swap: avoid a xa load for swapout path

From: Kairui Song <[email protected]>

A variable is never used for swapout path (shadowp is NULL) and compiler
is unable to optimize out the unneeded load since it's a function call.

Signed-off-by: Kairui Song <[email protected]>
---
mm/swap_state.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index b3b14bd0dd64..ab79ffb71736 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -109,9 +109,9 @@ int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
goto unlock;
for (i = 0; i < nr; i++) {
VM_BUG_ON_FOLIO(xas.xa_index != idx + i, folio);
- old = xas_load(&xas);
- if (xa_is_value(old)) {
- if (shadowp)
+ if (shadowp) {
+ old = xas_load(&xas);
+ if (xa_is_value(old))
*shadowp = old;
}
xas_store(&xas, folio);
--
2.42.0

2023-10-17 03:00:55

by Matthew Wilcox

Subject: Re: [PATCH] mm/swap: avoid a xa load for swapout path

On Tue, Oct 17, 2023 at 09:17:28AM +0800, Kairui Song wrote:
> From: Kairui Song <[email protected]>
>
> A variable is never used for swapout path (shadowp is NULL) and compiler
> is unable to optimize out the unneeded load since it's a function call.
>
> Signed-off-by: Kairui Song <[email protected]>

Reviewed-by: Matthew Wilcox (Oracle)

Possibly worth adding a reference to
3852f6768ede ("mm/swapcache: support to handle the shadow entries")

Not sure it's worth a Fixes:, but that's where it was introduced.