From a41f24ea9fd6169b147c53c2392e2887cc1d9247 Mon Sep 17 00:00:00 2001 From: Nishanth Aravamudan Date: Tue, 29 Apr 2008 00:58:25 -0700 Subject: page allocator: smarter retry of costly-order allocations Because of page order checks in __alloc_pages(), hugepage (and similarly large order) allocations will not retry unless explicitly marked __GFP_REPEAT. However, the current retry logic is nearly an infinite loop (or until reclaim does no progress whatsoever). For these costly allocations, that seems like overkill and could potentially never terminate. Mel observed that allowing current __GFP_REPEAT semantics for hugepage allocations essentially killed the system. I believe this is because we may continue to reclaim small orders of pages all over, but never have enough to satisfy the hugepage allocation request. This is clearly only a problem for large order allocations, of which hugepages are the most obvious (to me). Modify try_to_free_pages() to indicate how many pages were reclaimed. Use that information in __alloc_pages() to eventually fail a large __GFP_REPEAT allocation when we've reclaimed an order of pages equal to or greater than the allocation's order. This relies on lumpy reclaim functioning as advertised. Due to fragmentation, lumpy reclaim may not be able to free up the order needed in one invocation, so multiple iterations may be requred. In other words, the more fragmented memory is, the more retry attempts __GFP_REPEAT will make (particularly for higher order allocations). This changes the semantics of __GFP_REPEAT subtly, but *only* for allocations > PAGE_ALLOC_COSTLY_ORDER. With this patch, for those size allocations, we will try up to some point (at least 1< Cc: Andy Whitcroft Tested-by: Mel Gorman Cc: Dave Hansen Cc: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 22 +++++++++++++++++----- mm/vmscan.c | 7 +++++-- 2 files changed, 22 insertions(+), 7 deletions(-) (limited to 'mm') diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 6965be064a3..0a502e99ee2 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1461,7 +1461,8 @@ __alloc_pages_internal(gfp_t gfp_mask, unsigned int order, struct task_struct *p = current; int do_retry; int alloc_flags; - int did_some_progress; + unsigned long did_some_progress; + unsigned long pages_reclaimed = 0; might_sleep_if(wait); @@ -1611,15 +1612,26 @@ nofail_alloc: * Don't let big-order allocations loop unless the caller explicitly * requests that. Wait for some write requests to complete then retry. * - * In this implementation, either order <= PAGE_ALLOC_COSTLY_ORDER or - * __GFP_REPEAT mean __GFP_NOFAIL, but that may not be true in other + * In this implementation, order <= PAGE_ALLOC_COSTLY_ORDER + * means __GFP_NOFAIL, but that may not be true in other * implementations. + * + * For order > PAGE_ALLOC_COSTLY_ORDER, if __GFP_REPEAT is + * specified, then we retry until we no longer reclaim any pages + * (above), or we've reclaimed an order of pages at least as + * large as the allocation's order. In both cases, if the + * allocation still fails, we stop retrying. */ + pages_reclaimed += did_some_progress; do_retry = 0; if (!(gfp_mask & __GFP_NORETRY)) { - if ((order <= PAGE_ALLOC_COSTLY_ORDER) || - (gfp_mask & __GFP_REPEAT)) + if (order <= PAGE_ALLOC_COSTLY_ORDER) { do_retry = 1; + } else { + if (gfp_mask & __GFP_REPEAT && + pages_reclaimed < (1 << order)) + do_retry = 1; + } if (gfp_mask & __GFP_NOFAIL) do_retry = 1; } diff --git a/mm/vmscan.c b/mm/vmscan.c index eceac9f9032..12e8627c974 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1299,6 +1299,9 @@ static unsigned long shrink_zones(int priority, struct zonelist *zonelist, * hope that some of these pages can be written. But if the allocating task * holds filesystem locks which prevent writeout this might not work, and the * allocation attempt will fail. + * + * returns: 0, if no pages reclaimed + * else, the number of pages reclaimed */ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, struct scan_control *sc) @@ -1347,7 +1350,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, } total_scanned += sc->nr_scanned; if (nr_reclaimed >= sc->swap_cluster_max) { - ret = 1; + ret = nr_reclaimed; goto out; } @@ -1370,7 +1373,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, } /* top priority shrink_caches still had more to do? don't OOM, then */ if (!sc->all_unreclaimable && scan_global_lru(sc)) - ret = 1; + ret = nr_reclaimed; out: /* * Now that we've scanned all the zones at this priority level, note -- cgit v1.2.3