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Miao Xie

2010-Mar-25 12:27 UTC

[PATCH 01/18] btrfs: Remove u64 conversion for PAGE_CACHE_SIZE

From: Zhao Lei <zhaolei@cn.fujitsu.com>

We don''t need to convert PAGE_CACHE_SIZE to u64 in bit operation.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
---
 fs/btrfs/compression.c |    2 +-
 fs/btrfs/extent_io.c   |   16 ++++++++--------
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 28b92a7..467e631 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -349,7 +349,7 @@ int btrfs_submit_compressed_write(struct inode *inode, u64
start,
 	struct block_device *bdev;
 	int ret;
 
-	WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
+	WARN_ON(start & (PAGE_CACHE_SIZE - 1));
 	cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 	atomic_set(&cb->pending_bios, 0);
 	cb->errors = 0;
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index c99121a..bdfbfa6 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3489,7 +3489,7 @@ void read_extent_buffer(struct extent_buffer *eb, void
*dstv,
 	struct page *page;
 	char *kaddr;
 	char *dst = (char *)dstv;
-	size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
+	size_t start_offset = eb->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
 
 	WARN_ON(start > eb->len);
@@ -3520,7 +3520,7 @@ int map_private_extent_buffer(struct extent_buffer *eb,
unsigned long start,
 	size_t offset = start & (PAGE_CACHE_SIZE - 1);
 	char *kaddr;
 	struct page *p;
-	size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
+	size_t start_offset = eb->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
 	unsigned long end_i = (start_offset + start + min_len - 1) >>
 		PAGE_CACHE_SHIFT;
@@ -3589,7 +3589,7 @@ int memcmp_extent_buffer(struct extent_buffer *eb, const
void *ptrv,
 	struct page *page;
 	char *kaddr;
 	char *ptr = (char *)ptrv;
-	size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
+	size_t start_offset = eb->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
 	int ret = 0;
 
@@ -3625,7 +3625,7 @@ void write_extent_buffer(struct extent_buffer *eb, const
void *srcv,
 	struct page *page;
 	char *kaddr;
 	char *src = (char *)srcv;
-	size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
+	size_t start_offset = eb->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
 
 	WARN_ON(start > eb->len);
@@ -3656,7 +3656,7 @@ void memset_extent_buffer(struct extent_buffer *eb, char
c,
 	size_t offset;
 	struct page *page;
 	char *kaddr;
-	size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE - 1);
+	size_t start_offset = eb->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
 
 	WARN_ON(start > eb->len);
@@ -3688,7 +3688,7 @@ void copy_extent_buffer(struct extent_buffer *dst, struct
extent_buffer *src,
 	size_t offset;
 	struct page *page;
 	char *kaddr;
-	size_t start_offset = dst->start & ((u64)PAGE_CACHE_SIZE - 1);
+	size_t start_offset = dst->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long i = (start_offset + dst_offset) >> PAGE_CACHE_SHIFT;
 
 	WARN_ON(src->len != dst_len);
@@ -3757,7 +3757,7 @@ void memcpy_extent_buffer(struct extent_buffer *dst,
unsigned long dst_offset,
 	size_t cur;
 	size_t dst_off_in_page;
 	size_t src_off_in_page;
-	size_t start_offset = dst->start & ((u64)PAGE_CACHE_SIZE - 1);
+	size_t start_offset = dst->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long dst_i;
 	unsigned long src_i;
 
@@ -3804,7 +3804,7 @@ void memmove_extent_buffer(struct extent_buffer *dst,
unsigned long dst_offset,
 	size_t src_off_in_page;
 	unsigned long dst_end = dst_offset + len - 1;
 	unsigned long src_end = src_offset + len - 1;
-	size_t start_offset = dst->start & ((u64)PAGE_CACHE_SIZE - 1);
+	size_t start_offset = dst->start & (PAGE_CACHE_SIZE - 1);
 	unsigned long dst_i;
 	unsigned long src_i;
 
-- 
1.6.5.2


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Chris Mason

2010-Mar-25 13:02 UTC

head link

Re: [PATCH 01/18] btrfs: Remove u64 conversion for PAGE_CACHE_SIZE

On Thu, Mar 25, 2010 at 08:27:26PM +0800, Miao Xie
wrote:> From: Zhao Lei <zhaolei@cn.fujitsu.com>
> 
> We don''t need to convert PAGE_CACHE_SIZE to u64 in bit operation.
For code like this:

u64 size = (some number that doesn''t fit in 32 bits)

if (size & (PAGE_CACHE_SIZE - 1)) {
}

The answer should be the same either way.  But if the code gets
switched:

start = size & ~(PAGE_CACHE_SIZE - 1);

Some arches are going to get the wrong answer here.  We had a few bugs
like this early on and I went through and casted everything to be
consistent.  While this patch is correct, I would rather leave the casts
to avoid subtle problems later on as the code changes.

-chris

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Zhaolei

2010-Mar-31 04:04 UTC

head link

Re: Re: [PATCH 01/18] btrfs: Remove u64 conversion for PAGE_CACHE_SIZE

Chris Mason wrote:> On Thu, Mar 25, 2010 at 08:27:26PM +0800, Miao Xie wrote:
>> From: Zhao Lei <zhaolei@cn.fujitsu.com>
>>
>> We don''t need to convert PAGE_CACHE_SIZE to u64 in bit
operation.
> 
> For code like this:
> 
> u64 size = (some number that doesn''t fit in 32 bits)
> 
> if (size & (PAGE_CACHE_SIZE - 1)) {
> }
> 
> The answer should be the same either way.  But if the code gets
> switched:
> 
> start = size & ~(PAGE_CACHE_SIZE - 1);
> 
> Some arches are going to get the wrong answer here.  We had a few bugs
> like this early on and I went through and casted everything to be
> consistent.  While this patch is correct, I would rather leave the casts
> to avoid subtle problems later on as the code changes.
> 
> -chris
Hello, chris

Thanks for your explain.
I got your meaning.

But at least, we should make code unify:

// with u64:
[root@localhost btrfs]# grep ''((u64)PAGE_CACHE_SIZE - 1)'' *
compression.c:  WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
extent_io.c:    size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE -
1);
extent_io.c:    size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE -
1);
extent_io.c:    size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE -
1);
extent_io.c:    size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE -
1);
extent_io.c:    size_t start_offset = eb->start & ((u64)PAGE_CACHE_SIZE -
1);
extent_io.c:    size_t start_offset = dst->start & ((u64)PAGE_CACHE_SIZE
- 1);
extent_io.c:    size_t start_offset = dst->start & ((u64)PAGE_CACHE_SIZE
- 1);
extent_io.c:    size_t start_offset = dst->start & ((u64)PAGE_CACHE_SIZE
- 1);

// without u64:
[root@localhost btrfs]# grep ''(PAGE_CACHE_SIZE - 1)'' *
compression.c:                  size_t zero_offset = isize &
(PAGE_CACHE_SIZE - 1);
extent_io.c:                    unsigned long offset = (*start) &
(PAGE_CACHE_SIZE - 1);
extent_io.c:            size_t zero_offset = last_byte & (PAGE_CACHE_SIZE -
1);
extent_io.c:    pg_offset = i_size & (PAGE_CACHE_SIZE - 1);
extent_io.c:            block_off_start = block_start & (PAGE_CACHE_SIZE -
1);
extent_io.c:            page_offset = block_start & (PAGE_CACHE_SIZE - 1);
extent_io.c:            if ((i == 0 && (eb->start &
(PAGE_CACHE_SIZE - 1))) ||
extent_io.c:                 ((eb->start + eb->len) & (PAGE_CACHE_SIZE
- 1)))) {
extent_io.c:    size_t offset = start & (PAGE_CACHE_SIZE - 1);
file.c: int offset = pos & (PAGE_CACHE_SIZE - 1);
file.c: if ((pos & (PAGE_CACHE_SIZE - 1))) {
file.c: if ((pos + count) & (PAGE_CACHE_SIZE - 1)) {
file.c:         size_t offset = pos & (PAGE_CACHE_SIZE - 1);
file-item.c:            memcpy(eb_token + ((unsigned long)item &
(PAGE_CACHE_SIZE - 1)),
inode.c:                offset = start & (PAGE_CACHE_SIZE - 1);
inode.c:                                (PAGE_CACHE_SIZE - 1);
inode.c:                        ~(PAGE_CACHE_SIZE - 1);
inode.c:        if ((end & (PAGE_CACHE_SIZE - 1)) == 0)

Thanks
Zhaolei
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Btrfs devel - Mar 2010 - [PATCH 01/18] btrfs: Remove u64 conversion for PAGE_CACHE_SIZE

[PATCH 01/18] btrfs: Remove u64 conversion for PAGE_CACHE_SIZE

Re: [PATCH 01/18] btrfs: Remove u64 conversion for PAGE_CACHE_SIZE

Re: Re: [PATCH 01/18] btrfs: Remove u64 conversion for PAGE_CACHE_SIZE