[PATCH] mm: zbud: fix condition check on allocation size

[PATCH] mm: zbud: fix condition check on allocation size

[Heesub Shin]

zbud_alloc() incorrectly verifies the size of allocation limit. It
should deny the allocation request greater than (PAGE_SIZE -
ZHDR_SIZE_ALIGNED - CHUNK_SIZE), not (PAGE_SIZE - ZHDR_SIZE_ALIGNED)
which has no remaining spaces for its buddy. There is no point in
spending the entire zbud page storing only a single page, since we don't
have any benefits.

Signed-off-by: Heesub Shin <heesub.shin@samsung.com>
---
 mm/zbud.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/zbud.c b/mm/zbud.c
index 9bb4710..ad1e781 100644
--- a/mm/zbud.c
+++ b/mm/zbud.c
@@ -257,7 +257,7 @@ int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
 
 	if (size <= 0 || gfp & __GFP_HIGHMEM)
 		return -EINVAL;
-	if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED)
+	if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
 		return -ENOSPC;
 	chunks = size_to_chunks(size);
 	spin_lock(&pool->lock);
-- 
1.8.3.2

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Re: [PATCH] mm: zbud: fix condition check on allocation size

[Bob Liu]

On 07/17/2013 10:30 PM, Heesub Shin wrote:
> zbud_alloc() incorrectly verifies the size of allocation limit. It
> should deny the allocation request greater than (PAGE_SIZE -
> ZHDR_SIZE_ALIGNED - CHUNK_SIZE), not (PAGE_SIZE - ZHDR_SIZE_ALIGNED)
> which has no remaining spaces for its buddy. There is no point in
> spending the entire zbud page storing only a single page, since we don't
> have any benefits.
> 
> Signed-off-by: Heesub Shin <heesub.shin@samsung.com>

Looks good to me, although I'm thinking to make it more aggressive.
eg. minus two or three times of CHUNK_SIZE.

> ---
>  mm/zbud.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/zbud.c b/mm/zbud.c
> index 9bb4710..ad1e781 100644
> --- a/mm/zbud.c
> +++ b/mm/zbud.c
> @@ -257,7 +257,7 @@ int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
>  
>  	if (size <= 0 || gfp & __GFP_HIGHMEM)
>  		return -EINVAL;
> -	if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED)
> +	if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
>  		return -ENOSPC;
>  	chunks = size_to_chunks(size);
>  	spin_lock(&pool->lock);
> 

-- 
Regards,
-Bob

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