Re: [PATCH 1/5] page allocator: Always wake kswapd when restarting an allocation attempt after direct reclaim failed
From: KOSAKI Motohiro <hidden>
Date: 2009-10-26 01:11:30
Also in:
linux-mm, lkml
Subsystem:
memory management, memory management - page allocator, the rest · Maintainers:
Andrew Morton, Vlastimil Babka, Linus Torvalds
quoted hunk ↗ jump to hunk
If a direct reclaim makes no forward progress, it considers whether it should go OOM or not. Whether OOM is triggered or not, it may retry the application afterwards. In times past, this would always wake kswapd as well but currently, kswapd is not woken up after direct reclaim fails. For order-0 allocations, this makes little difference but if there is a heavy mix of higher-order allocations that direct reclaim is failing for, it might mean that kswapd is not rewoken for higher orders as much as it did previously. This patch wakes up kswapd when an allocation is being retried after a direct reclaim failure. It would be expected that kswapd is already awake, but this has the effect of telling kswapd to reclaim at the higher order as well. Signed-off-by: Mel Gorman <redacted> --- mm/page_alloc.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)diff --git a/mm/page_alloc.c b/mm/page_alloc.c index bf72055..dfa4362 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c@@ -1817,9 +1817,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, if (NUMA_BUILD && (gfp_mask & GFP_THISNODE) == GFP_THISNODE) goto nopage; +restart: wake_all_kswapd(order, zonelist, high_zoneidx); -restart: /* * OK, we're below the kswapd watermark and have kicked background * reclaim. Now things get more complex, so set up alloc_flags according
I think this patch is correct. personally, I like to add some commnent at restart label. but it isn't big matter. Reviewed-by: KOSAKI Motohiro [off-list ref] However, I have a question. __alloc_pages_slowpath() retry logic is, 1. try_to_free_pages() reclaimed some pages: -> wait awhile and goto rebalance 2. try_to_free_pages() didn't reclaimed any page: -> call out_of_memory() and goto restart Then, case-1 should be fixed too? I mean,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bf72055..5a27896 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c@@ -1899,6 +1899,12 @@ rebalance: if (should_alloc_retry(gfp_mask, order, pages_reclaimed)) { /* Wait for some write requests to complete then retry */ congestion_wait(BLK_RW_ASYNC, HZ/50); + + /* + * While we wait congestion wait, Amount of free memory can + * be changed dramatically. Thus, we kick kswapd again. + */ + wake_all_kswapd(order, zonelist, high_zoneidx); goto rebalance; } -------------------------------------------
?