Re: [PATCH] direct-io: Using kmem_cache_zalloc() instead of kmem_cache_alloc() and memset()
From: Jeff Moyer
Date: Thu Feb 25 2021 - 10:47:43 EST
Y, Yang,
Yang Li <yang.lee@xxxxxxxxxxxxxxxxx> writes:
>
Fix the following coccicheck warning:
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./fs/direct-io.c:1155:7-23: WARNING: kmem_cache_zalloc should be used
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for dio, instead of kmem_cache_alloc/memset
>
>
Reported-by: Abaci Robot <abaci@xxxxxxxxxxxxxxxxx>
>
Signed-off-by: Yang Li <yang.lee@xxxxxxxxxxxxxxxxx>
>
---
>
fs/direct-io.c | 4 +---
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1 file changed, 1 insertion(+), 3 deletions(-)
>
>
diff --git a/fs/direct-io.c b/fs/direct-io.c
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index 0957e1b..6ec2935 100644
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--- a/fs/direct-io.c
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+++ b/fs/direct-io.c
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@@ -1152,7 +1152,7 @@ static inline int drop_refcount(struct dio *dio)
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if (iov_iter_rw(iter) == READ && !count)
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return 0;
>
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- dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
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+ dio = kmem_cache_zalloc(dio_cache, GFP_KERNEL);
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if (!dio)
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return -ENOMEM;
>
/*
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@@ -1160,8 +1160,6 @@ static inline int drop_refcount(struct dio *dio)
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* performance regression in a database benchmark. So, we take
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* care to only zero out what's needed.
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*/
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- memset(dio, 0, offsetof(struct dio, pages));
>
-
You must have missed the comment just above this memset:
/*
* Believe it or not, zeroing out the page array caused a .5%
* performance regression in a database benchmark. So, we take
* care to only zero out what's needed.
*/
That's referring to this part of the dio struct:
/*
* pages[] (and any fields placed after it) are not zeroed out at
* allocation time. Don't add new fields after pages[] unless you
* wish that they not be zeroed.
*/
union {
struct page *pages[DIO_PAGES]; /* page buffer */
struct work_struct complete_work;/* deferred AIO completion */
};
} ____cacheline_aligned_in_smp;
Nacked-by: Jeff Moyer <jmoyer@xxxxxxxxxx>