From 753791910e23a95aade78f69e49713acddf8bb8c Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Wed, 11 Feb 2015 15:25:38 -0800 Subject: [PATCH] mm: set page->pfmemalloc in prep_new_page() The possibility of replacing the numerous parameters of alloc_pages* functions with a single structure has been discussed when Minchan proposed to expand the x86 kernel stack [1]. This series implements the change, along with few more cleanups/microoptimizations. The series is based on next-20150108 and I used gcc 4.8.3 20140627 on openSUSE 13.2 for compiling. Config includess NUMA and COMPACTION. The core change is the introduction of a new struct alloc_context, which looks like this: struct alloc_context { struct zonelist *zonelist; nodemask_t *nodemask; struct zone *preferred_zone; int classzone_idx; int migratetype; enum zone_type high_zoneidx; }; All the contents is mostly constant, except that __alloc_pages_slowpath() changes preferred_zone, classzone_idx and potentially zonelist. But that's not a problem in case control returns to retry_cpuset: in __alloc_pages_nodemask(), those will be reset to initial values again (although it's a bit subtle). On the other hand, gfp_flags and alloc_info mutate so much that it doesn't make sense to put them into alloc_context. Still, the result is one parameter instead of up to 7. This is all in Patch 2. Patch 3 is a step to expand alloc_context usage out of page_alloc.c itself. The function try_to_compact_pages() can also much benefit from the parameter reduction, but it means the struct definition has to be moved to a shared header. Patch 1 should IMHO be included even if the rest is deemed not useful enough. It improves maintainability and also has some code/stack reduction. Patch 4 is OTOH a tiny optimization. Overall bloat-o-meter results: add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-460 (-460) function old new delta nr_free_zone_pages 129 115 -14 __alloc_pages_direct_compact 329 256 -73 get_page_from_freelist 2670 2576 -94 __alloc_pages_nodemask 2564 2285 -279 try_to_compact_pages 582 579 -3 Overall stack sizes per ./scripts/checkstack.pl: old new delta get_page_from_freelist: 184 184 0 __alloc_pages_nodemask 248 200 -48 __alloc_pages_direct_c 40 - -40 try_to_compact_pages 72 72 0 -88 [1] http://marc.info/?l=linux-mm&m=140142462528257&w=2 This patch (of 4): prep_new_page() sets almost everything in the struct page of the page being allocated, except page->pfmemalloc. This is not obvious and has at least once led to a bug where page->pfmemalloc was forgotten to be set correctly, see commit 8fb74b9fb2b1 ("mm: compaction: partially revert capture of suitable high-order page"). This patch moves the pfmemalloc setting to prep_new_page(), which means it needs to gain alloc_flags parameter. The call to prep_new_page is moved from buffered_rmqueue() to get_page_from_freelist(), which also leads to simpler code. An obsolete comment for buffered_rmqueue() is replaced. In addition to better maintainability there is a small reduction of code and stack usage for get_page_from_freelist(), which inlines the other functions involved. add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-145 (-145) function old new delta get_page_from_freelist 2670 2525 -145 Stack usage is reduced from 184 to 168 bytes. Signed-off-by: Vlastimil Babka Acked-by: Michal Hocko Cc: Mel Gorman Cc: Zhang Yanfei Cc: Minchan Kim Cc: David Rientjes Cc: Rik van Riel Cc: "Aneesh Kumar K.V" Cc: "Kirill A. Shutemov" Cc: Johannes Weiner Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 37 ++++++++++++++++--------------------- 1 file changed, 16 insertions(+), 21 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index a88cb0c..30a3250 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -970,7 +970,8 @@ static inline int check_new_page(struct page *page) return 0; } -static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags) +static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags, + int alloc_flags) { int i; @@ -994,6 +995,14 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags) set_page_owner(page, order, gfp_flags); + /* + * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was necessary to + * allocate the page. The expectation is that the caller is taking + * steps that will free more memory. The caller should avoid the page + * being used for !PFMEMALLOC purposes. + */ + page->pfmemalloc = !!(alloc_flags & ALLOC_NO_WATERMARKS); + return 0; } @@ -1642,9 +1651,7 @@ int split_free_page(struct page *page) } /* - * Really, prep_compound_page() should be called from __rmqueue_bulk(). But - * we cheat by calling it from here, in the order > 0 path. Saves a branch - * or two. + * Allocate a page from the given zone. Use pcplists for order-0 allocations. */ static inline struct page *buffered_rmqueue(struct zone *preferred_zone, @@ -1655,7 +1662,6 @@ struct page *buffered_rmqueue(struct zone *preferred_zone, struct page *page; bool cold = ((gfp_flags & __GFP_COLD) != 0); -again: if (likely(order == 0)) { struct per_cpu_pages *pcp; struct list_head *list; @@ -1711,8 +1717,6 @@ again: local_irq_restore(flags); VM_BUG_ON_PAGE(bad_range(zone, page), page); - if (prep_new_page(page, order, gfp_flags)) - goto again; return page; failed: @@ -2177,25 +2181,16 @@ zonelist_scan: try_this_zone: page = buffered_rmqueue(preferred_zone, zone, order, gfp_mask, migratetype); - if (page) - break; + if (page) { + if (prep_new_page(page, order, gfp_mask, alloc_flags)) + goto try_this_zone; + return page; + } this_zone_full: if (IS_ENABLED(CONFIG_NUMA) && zlc_active) zlc_mark_zone_full(zonelist, z); } - if (page) { - /* - * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was - * necessary to allocate the page. The expectation is - * that the caller is taking steps that will free more - * memory. The caller should avoid the page being used - * for !PFMEMALLOC purposes. - */ - page->pfmemalloc = !!(alloc_flags & ALLOC_NO_WATERMARKS); - return page; - } - /* * The first pass makes sure allocations are spread fairly within the * local node. However, the local node might have free pages left -- 2.7.4