From 10f396de0b94dd4180d8a589d5dc510eff65eac5 Mon Sep 17 00:00:00 2001 From: Roman Pen Date: Wed, 15 Apr 2015 16:13:55 -0700 Subject: [PATCH] mm/vmalloc: get rid of dirty bitmap inside vmap_block structure In original implementation of vm_map_ram made by Nick Piggin there were two bitmaps: alloc_map and dirty_map. None of them were used as supposed to be: finding a suitable free hole for next allocation in block. vm_map_ram allocates space sequentially in block and on free call marks pages as dirty, so freed space can't be reused anymore. Actually it would be very interesting to know the real meaning of those bitmaps, maybe implementation was incomplete, etc. But long time ago Zhang Yanfei removed alloc_map by these two commits: mm/vmalloc.c: remove dead code in vb_alloc 21a9f7b698ca4d18e3c9c74586723f73baeeecf0 mm/vmalloc.c: remove alloc_map from vmap_block 352c5c4c941daaf942a9d4be80cccc62201809e9 In this patch I replaced dirty_map with two range variables: dirty min and max. These variables store minimum and maximum position of dirty space in a block, since we need only to know the dirty range, not exact position of dirty pages. Why it was made? Several reasons: at first glance it seems that vm_map_ram allocator concerns about fragmentation thus it uses bitmaps for finding free hole, but it is not true. To avoid complexity seems it is better to use something simple, like min or max range values. Secondly, code also becomes simpler, without iteration over bitmap, just comparing values in min and max macros. Thirdly, bitmap occupies up to 1024 bits (4MB is a max size of a block). Here I replaced the whole bitmap with two longs. Finally vm_unmap_aliases should be slightly faster and the whole vmap_block structure occupies less memory. Signed-off-by: Roman Pen Cc: Zhang Yanfei Cc: Eric Dumazet Acked-by: Joonsoo Kim Cc: David Rientjes Cc: WANG Chao Cc: Fabian Frederick Cc: Christoph Lameter Cc: Gioh Kim Cc: Rob Jones Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmalloc.c | 35 +++++++++++++++++------------------ 1 file changed, 17 insertions(+), 18 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 21ec16b7e6e15..2faaa2976447a 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -765,7 +765,7 @@ struct vmap_block { spinlock_t lock; struct vmap_area *va; unsigned long free, dirty; - DECLARE_BITMAP(dirty_map, VMAP_BBMAP_BITS); + unsigned long dirty_min, dirty_max; /*< dirty range */ struct list_head free_list; struct rcu_head rcu_head; struct list_head purge; @@ -851,7 +851,8 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask) BUG_ON(VMAP_BBMAP_BITS <= (1UL << order)); vb->free = VMAP_BBMAP_BITS - (1UL << order); vb->dirty = 0; - bitmap_zero(vb->dirty_map, VMAP_BBMAP_BITS); + vb->dirty_min = VMAP_BBMAP_BITS; + vb->dirty_max = 0; INIT_LIST_HEAD(&vb->free_list); vb_idx = addr_to_vb_idx(va->va_start); @@ -902,7 +903,8 @@ static void purge_fragmented_blocks(int cpu) if (vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS) { vb->free = 0; /* prevent further allocs after releasing lock */ vb->dirty = VMAP_BBMAP_BITS; /* prevent purging it again */ - bitmap_fill(vb->dirty_map, VMAP_BBMAP_BITS); + vb->dirty_min = 0; + vb->dirty_max = VMAP_BBMAP_BITS; spin_lock(&vbq->lock); list_del_rcu(&vb->free_list); spin_unlock(&vbq->lock); @@ -995,6 +997,7 @@ static void vb_free(const void *addr, unsigned long size) order = get_order(size); offset = (unsigned long)addr & (VMAP_BLOCK_SIZE - 1); + offset >>= PAGE_SHIFT; vb_idx = addr_to_vb_idx((unsigned long)addr); rcu_read_lock(); @@ -1005,7 +1008,10 @@ static void vb_free(const void *addr, unsigned long size) vunmap_page_range((unsigned long)addr, (unsigned long)addr + size); spin_lock(&vb->lock); - BUG_ON(bitmap_allocate_region(vb->dirty_map, offset >> PAGE_SHIFT, order)); + + /* Expand dirty range */ + vb->dirty_min = min(vb->dirty_min, offset); + vb->dirty_max = max(vb->dirty_max, offset + (1UL << order)); vb->dirty += 1UL << order; if (vb->dirty == VMAP_BBMAP_BITS) { @@ -1044,25 +1050,18 @@ void vm_unmap_aliases(void) rcu_read_lock(); list_for_each_entry_rcu(vb, &vbq->free, free_list) { - int i, j; - spin_lock(&vb->lock); - i = find_first_bit(vb->dirty_map, VMAP_BBMAP_BITS); - if (i < VMAP_BBMAP_BITS) { + if (vb->dirty) { + unsigned long va_start = vb->va->va_start; unsigned long s, e; - j = find_last_bit(vb->dirty_map, - VMAP_BBMAP_BITS); - j = j + 1; /* need exclusive index */ + s = va_start + (vb->dirty_min << PAGE_SHIFT); + e = va_start + (vb->dirty_max << PAGE_SHIFT); - s = vb->va->va_start + (i << PAGE_SHIFT); - e = vb->va->va_start + (j << PAGE_SHIFT); - flush = 1; + start = min(s, start); + end = max(e, end); - if (s < start) - start = s; - if (e > end) - end = e; + flush = 1; } spin_unlock(&vb->lock); } -- 2.39.5