linux-kernel - Re: [PATCH] Remove needless lock and list in vmap

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Date:	Wed, 7 Jan 2009 16:45:18 +0900
From:	MinChan Kim <minchan.kim@...il.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	stable@...nel.org,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Remove needless lock and list in vmap

* Nick Piggin (npiggin@...e.de) wrote:
> On Wed, Jan 07, 2009 at 02:47:13PM +0900, MinChan Kim wrote:
> > Anyone don't use vmap's dirty_list.
> > I am not sure this is thing Nick's future work on purpose.
> > If it is a dummy, we can remove dirty list and related codes
> > to handle list and locking.
> > 
> > Also, In free_vmap_block, we don't have to check empty free_list.
> > That's becuase before calling free_vmap_block, vb_free always checks
> > empty of vb->free_list.
> > 
> > Now except vb_free, Anywhere don't call free_vmap_block.
> > so, we can remove that check and locking.
> > 
> > If it is nick's intention to work in future, please, ignore this patch. 
> 
> It was going to be an attempt to optimise flushing a bit, but I never
> finished writing the code. Either way, it doesn't belong upstream until
> time as it is needed, so your patch is good.

Thanks for your kind words. 
 
> Can you just put a BUG_ON(!list_empty(&vb->free_list)); in free_vmap_block?
> Then add Acked-by: Nick Piggin <npiggin@...e.de>

I added BUG_ON.

> Thanks,
> Nick
> 

This is improvement patch. 

===


Subject: [PATCH] Remove needless lock and list in vmap

Now, Anyone don't use vmap's dirty_list.
It's for optimizing flushing. but Nick didn't write the code yet.
so, we don't need it until time as it is needed.

This patch removes vmap_block's dirty_list and codes related to it.

Signed-off-by: MinChan Kim <minchan.kim@...il.com>
Acked-by: Nick Piggin <npiggin@...e.de>
---
 mm/vmalloc.c |   19 +++----------------
 1 files changed, 3 insertions(+), 16 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 1ddb77b..a7e1c2e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -629,10 +629,7 @@ struct vmap_block {
 	DECLARE_BITMAP(alloc_map, VMAP_BBMAP_BITS);
 	DECLARE_BITMAP(dirty_map, VMAP_BBMAP_BITS);
 	union {
-		struct {
-			struct list_head free_list;
-			struct list_head dirty_list;
-		};
+		struct list_head free_list;
 		struct rcu_head rcu_head;
 	};
 };
@@ -699,7 +696,6 @@ static struct vmap_block *new_vmap_block(gfp_t gfp_mask)
 	bitmap_zero(vb->alloc_map, VMAP_BBMAP_BITS);
 	bitmap_zero(vb->dirty_map, VMAP_BBMAP_BITS);
 	INIT_LIST_HEAD(&vb->free_list);
-	INIT_LIST_HEAD(&vb->dirty_list);
 
 	vb_idx = addr_to_vb_idx(va->va_start);
 	spin_lock(&vmap_block_tree_lock);
@@ -730,12 +726,7 @@ static void free_vmap_block(struct vmap_block *vb)
 	struct vmap_block *tmp;
 	unsigned long vb_idx;
 
-	spin_lock(&vb->vbq->lock);
-	if (!list_empty(&vb->free_list))
-		list_del(&vb->free_list);
-	if (!list_empty(&vb->dirty_list))
-		list_del(&vb->dirty_list);
-	spin_unlock(&vb->vbq->lock);
+	BUG_ON(!list_empty(&vb->free_list));
 
 	vb_idx = addr_to_vb_idx(vb->va->va_start);
 	spin_lock(&vmap_block_tree_lock);
@@ -820,11 +811,7 @@ static void vb_free(const void *addr, unsigned long size)
 
 	spin_lock(&vb->lock);
 	bitmap_allocate_region(vb->dirty_map, offset >> PAGE_SHIFT, order);
-	if (!vb->dirty) {
-		spin_lock(&vb->vbq->lock);
-		list_add(&vb->dirty_list, &vb->vbq->dirty);
-		spin_unlock(&vb->vbq->lock);
-	}
+
 	vb->dirty += 1UL << order;
 	if (vb->dirty == VMAP_BBMAP_BITS) {
 		BUG_ON(vb->free || !list_empty(&vb->free_list));
-- 
1.5.4.3

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