From 248ac0e1943ad1796393d281b096184719eb3f97 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Tue, 24 May 2011 17:11:43 -0700 Subject: [PATCH] mm/vmalloc: remove guard page from between vmap blocks The vmap allocator is used to, among other things, allocate per-cpu vmap blocks, where each vmap block is naturally aligned to its own size. Obviously, leaving a guard page after each vmap area forbids packing vmap blocks efficiently and can make the kernel run out of possible vmap blocks long before overall vmap space is exhausted. The new interface to map a user-supplied page array into linear vmalloc space (vm_map_ram) insists on allocating from a vmap block (instead of falling back to a custom area) when the area size is below a certain threshold. With heavy users of this interface (e.g. XFS) and limited vmalloc space on 32-bit, vmap block exhaustion is a real problem. Remove the guard page from the core vmap allocator. vmalloc and the old vmap interface enforce a guard page on their own at a higher level. Note that without this patch, we had accidental guard pages after those vm_map_ram areas that happened to be at the end of a vmap block, but not between every area. This patch removes this accidental guard page only. If we want guard pages after every vm_map_ram area, this should be done separately. And just like with vmalloc and the old interface on a different level, not in the core allocator. Mel pointed out: "If necessary, the guard page could be reintroduced as a debugging-only option (CONFIG_DEBUG_PAGEALLOC?). Otherwise it seems reasonable." Signed-off-by: Johannes Weiner Cc: Nick Piggin Cc: Dave Chinner Acked-by: Mel Gorman Cc: Hugh Dickins Cc: Christoph Hellwig Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmalloc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 5d6030235d7a..4581ddcdda50 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -375,7 +375,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size, /* find starting point for our search */ if (free_vmap_cache) { first = rb_entry(free_vmap_cache, struct vmap_area, rb_node); - addr = ALIGN(first->va_end + PAGE_SIZE, align); + addr = ALIGN(first->va_end, align); if (addr < vstart) goto nocache; if (addr + size - 1 < addr) @@ -406,10 +406,10 @@ static struct vmap_area *alloc_vmap_area(unsigned long size, } /* from the starting point, walk areas until a suitable hole is found */ - while (addr + size >= first->va_start && addr + size <= vend) { + while (addr + size > first->va_start && addr + size <= vend) { if (addr + cached_hole_size < first->va_start) cached_hole_size = first->va_start - addr; - addr = ALIGN(first->va_end + PAGE_SIZE, align); + addr = ALIGN(first->va_end, align); if (addr + size - 1 < addr) goto overflow; -- GitLab