On 11/11/20 9:17 AM, huang ying wrote:
On Thu, Nov 5, 2020 at 4:56 PM Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> wrote:
From: Hugh Dickins <hughd@xxxxxxxxxx>
It is necessary for page_idle_get_page() to recheck PageLRU() after
get_page_unless_zero(), but holding lru_lock around that serves no
useful purpose, and adds to lru_lock contention: delete it.
See https://lore.kernel.org/lkml/20150504031722.GA2768@blaptop for the
discussion that led to lru_lock there; but __page_set_anon_rmap() now
uses WRITE_ONCE(), and I see no other risk in page_idle_clear_pte_refs()
using rmap_walk() (beyond the risk of racing PageAnon->PageKsm, mostly
but not entirely prevented by page_count() check in ksm.c's
write_protect_page(): that risk being shared with page_referenced() and
not helped by lru_lock).
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
mm/page_idle.c | 4 ----
1 file changed, 4 deletions(-)
diff --git a/mm/page_idle.c b/mm/page_idle.c
index 057c61df12db..64e5344a992c 100644
--- a/mm/page_idle.c
+++ b/mm/page_idle.c
@@ -32,19 +32,15 @@
static struct page *page_idle_get_page(unsigned long pfn)
{
struct page *page = pfn_to_online_page(pfn);
- pg_data_t *pgdat;
if (!page || !PageLRU(page) ||
!get_page_unless_zero(page))
return NULL;
- pgdat = page_pgdat(page);
- spin_lock_irq(&pgdat->lru_lock);
get_page_unless_zero() is a full memory barrier. But do we need a
compiler barrier here to prevent the compiler to cache PageLRU()
results here? Otherwise looks OK to me,
I think the compiler barrier is also implied by the full memory barrier and
prevents the caching.
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Best Regards,
Huang, Ying
if (unlikely(!PageLRU(page))) {
put_page(page);
page = NULL;
}
- spin_unlock_irq(&pgdat->lru_lock);
return page;
}
--
1.8.3.1
