Re: [PATCH] mm: add free_hot_cold_page_list helper
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2011-08-26 22:21:40
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On Fri, 29 Jul 2011 11:58:37 +0400 Konstantin Khlebnikov [off-list ref] wrote:
This patch adds helper free_hot_cold_page_list() to free list of 0-order pages. It frees pages directly from list without temporary page-vector. It also calls trace_mm_pagevec_free() to simulate pagevec_free() behaviour. bloat-o-meter: add/remove: 1/1 grow/shrink: 1/3 up/down: 267/-295 (-28) function old new delta free_hot_cold_page_list - 264 +264 get_page_from_freelist 2129 2132 +3 __pagevec_free 243 239 -4 split_free_page 380 373 -7 release_pages 606 510 -96 free_page_list 188 - -188
It saves a total of 150 bytes for me.
quoted hunk ↗ jump to hunk
index cb40892..dd7b9cc 100644--- a/include/linux/gfp.h +++ b/include/linux/gfp.h@@ -358,6 +358,7 @@ void *alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask); extern void __free_pages(struct page *page, unsigned int order); extern void free_pages(unsigned long addr, unsigned int order); extern void free_hot_cold_page(struct page *page, int cold); +extern void free_hot_cold_page_list(struct list_head *list, int cold); #define __free_page(page) __free_pages((page), 0) #define free_page(addr) free_pages((addr), 0)diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 1dbcf88..af486e4 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c@@ -1209,6 +1209,18 @@ out: local_irq_restore(flags); } +void free_hot_cold_page_list(struct list_head *list, int cold) +{ + struct page *page, *next; + + list_for_each_entry_safe(page, next, list, lru) { + trace_mm_pagevec_free(page, cold); + free_hot_cold_page(page, cold); + } + + INIT_LIST_HEAD(list); +} + /* * split_page takes a non-compound higher-order page, and splits it into * n (1<<order) sub-pages: page[0..n]diff --git a/mm/swap.c b/mm/swap.c index 3a442f1..b9138c7 100644 --- a/mm/swap.c +++ b/mm/swap.c@@ -562,11 +562,10 @@ int lru_add_drain_all(void) void release_pages(struct page **pages, int nr, int cold) { int i; - struct pagevec pages_to_free; + LIST_HEAD(pages_to_free); struct zone *zone = NULL; unsigned long uninitialized_var(flags); - pagevec_init(&pages_to_free, cold); for (i = 0; i < nr; i++) { struct page *page = pages[i];@@ -597,19 +596,12 @@ void release_pages(struct page **pages, int nr, int cold) del_page_from_lru(zone, page); } - if (!pagevec_add(&pages_to_free, page)) { - if (zone) { - spin_unlock_irqrestore(&zone->lru_lock, flags); - zone = NULL; - } - __pagevec_free(&pages_to_free); - pagevec_reinit(&pages_to_free); - } + list_add_tail(&page->lru, &pages_to_free);
There's a potential problem here with cache longevity. If release_pages() is called with a large number of pages then the current code's approach of freeing pages 16-at-a-time will hopefully cause those pageframes to still be in CPU cache when we get to actually freeing them. But after this change, we free all the pages in a single operation right at the end, which adds risk that we'll have to reload all their pageframes into CPU cache again. That'll only be a problem if release_pages() _is_ called with a large number of pages. And manipulating large numbers of pages represents a lot of work, so the additional work from one cachemiss per page will presumably be tiny. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>