From 51c6f666fceb3184eeff045dad4432b602cd648e Mon Sep 17 00:00:00 2001 From: Robin Holt Date: Sun, 13 Nov 2005 16:06:42 -0800 Subject: [PATCH] mm: ZAP_BLOCK causes redundant work The address based work estimate for unmapping (for lockbreak) is and always was horribly inefficient for sparse mappings. The problem is most simply explained with an example: If we find a pgd is clear, we still have to call into unmap_page_range PGDIR_SIZE / ZAP_BLOCK_SIZE times, each time checking the clear pgd, in order to progress the working address to the next pgd. The fundamental way to solve the problem is to keep track of the end address we've processed and pass it back to the higher layers. From: Nick Piggin Modification to completely get away from address based work estimate and instead use an abstract count, with a very small cost for empty entries as opposed to present pages. On 2.6.14-git2, ppc64, and CONFIG_PREEMPT=y, mapping and unmapping 1TB of virtual address space takes 1.69s; with the following patch applied, this operation can be done 1000 times in less than 0.01s From: Andrew Morton With CONFIG_HUTETLB_PAGE=n: mm/memory.c: In function `unmap_vmas': mm/memory.c:779: warning: division by zero Due to zap_work -= (end - start) / (HPAGE_SIZE / PAGE_SIZE); So make the dummy HPAGE_SIZE non-zero Signed-off-by: Robin Holt Signed-off-by: Nick Piggin Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/hugetlb.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 0cea162b08c..1056717ee50 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -102,8 +102,8 @@ static inline unsigned long hugetlb_total_pages(void) #define hugetlb_fault(mm, vma, addr, write) ({ BUG(); 0; }) #ifndef HPAGE_MASK -#define HPAGE_MASK 0 /* Keep the compiler happy */ -#define HPAGE_SIZE 0 +#define HPAGE_MASK PAGE_MASK /* Keep the compiler happy */ +#define HPAGE_SIZE PAGE_SIZE #endif #endif /* !CONFIG_HUGETLB_PAGE */ -- cgit v1.2.3