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Date: Sat, 14 Jul 2007 00:54:35 -0500 From: Matt Mackall <mpm@...enic.com> To: linux-kernel <linux-kernel@...r.kernel.org> Cc: Nick Piggin <nickpiggin@...oo.com.au>, akpm@...ux-foundation.org, Pekka Enberg <penberg@...helsinki.fi>, Christoph Lameter <clameter@....com> Subject: [PATCH] slob: reduce list scanning The version of SLOB in -mm always scans its free list from the beginning, which results in small allocations and free segments clustering at the beginning of the list over time. This causes the average search to scan over a large stretch at the beginning on each allocation. By starting each page search where the last one left off, we evenly distribute the allocations and greatly shorten the average search. Without this patch, kernel compiles on a 1.5G machine take a large amount of system time for list scanning. With this patch, compiles are within a few seconds of performance of a SLAB kernel with no notable change in system time. Signed-off-by: Matt Mackall <mpm@...enic.com> Index: mm/mm/slob.c =================================================================== --- mm.orig/mm/slob.c 2007-07-13 17:51:25.000000000 -0500 +++ mm/mm/slob.c 2007-07-13 18:42:59.000000000 -0500 @@ -293,6 +293,7 @@ static void *slob_page_alloc(struct slob static void *slob_alloc(size_t size, gfp_t gfp, int align, int node) { struct slob_page *sp; + struct list_head *prev; slob_t *b = NULL; unsigned long flags; @@ -307,12 +308,22 @@ static void *slob_alloc(size_t size, gfp if (node != -1 && page_to_nid(&sp->page) != node) continue; #endif + /* Enough room on this page? */ + if (sp->units < SLOB_UNITS(size)) + continue; - if (sp->units >= SLOB_UNITS(size)) { - b = slob_page_alloc(sp, size, align); - if (b) - break; - } + /* Attempt to alloc */ + prev = sp->list.prev; + b = slob_page_alloc(sp, size, align); + if (!b) + continue; + + /* Improve fragment distribution and reduce our average + * search time by starting our next search here. (see + * Knuth vol 1, sec 2.5, pg 449) */ + if (free_slob_pages.next != prev->next) + list_move_tail(&free_slob_pages, prev->next); + break; } spin_unlock_irqrestore(&slob_lock, flags); -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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