Re: [PATCH] read-cache.c: fix index memory allocation

From: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Date: Oct 25, 2011, 18:00 UTC
Message-ID: <4EA6F924.6060208@lsrfire.ath.cx>
In-Reply-To: <CACsJy8A7yVk15aAgqDkKTz31rChA7Oj-kS2VT2y2tWS6h01GyA@mail.gmail.com>

Am 25.10.2011 02:01, schrieb Nguyen Thai Ngoc Duy:

Show 13 quoted lines

> On Tue, Oct 25, 2011 at 10:34 AM, Nguyen Thai Ngoc Duy
> <pclouds@gmail.com> wrote:
>> "git status" is slow. If your changes causes slowdown, it won't likely
>> stand out while other fast commands may show (read_cache() is used in
>> nearly all commands). So I tested using the following patch.
>>
>> The result on linux-2.6 shows about 10-20 us slowdown per each
>> read_cache() call (30-40 us on webkit, ~50k files) I think your patch
>> is good enough :-)
> 
> That was with -O0 by the way. valgrind/massif shows about 200kb memory
> more with your patch on webkit repository (7.497 MB vs 7.285 MB),
> using the same test, so memory overhead is ok too.

We can reduce that a bit -- unless block allocation of index entries is still done somewhere.

-- >8 --
Subject: [PATCH 2/1] cache.h: put single NUL at end of struct cache_entry

Since in-memory index entries are allocated individually now, the variable slack at the end meant to provide an eight byte alignment is not needed anymore. Have a single NUL instead. This saves zero to seven bytes for an entry, depending on its filename length.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
---

 cache.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/cache.h b/cache.h
index ec0e571..bd106b5 100644
--- a/cache.h
+++ b/cache.h
@@ -306,7 +306,7 @@ static inline unsigned int canon_mode(unsigned int mode)
 }
 
 #define flexible_size(STRUCT,len) ((offsetof(struct STRUCT,name) + (len) + 8) & ~7)
-#define cache_entry_size(len) flexible_size(cache_entry,len)
+#define cache_entry_size(len) (offsetof(struct cache_entry,name) + (len) + 1)
 #define ondisk_cache_entry_size(len) flexible_size(ondisk_cache_entry,len)
 #define ondisk_cache_entry_extended_size(len) flexible_size(ondisk_cache_entry_extended,len)

-- 
1.7.7