Re: [PATCH 04/12] bloom: clear each bloom_key after use

> On Fri, Apr 09, 2021 at 06:47:23PM +0000, Andrzej Hunt via GitGitGadget wrote:
>> From: Andrzej Hunt <ajrhunt@google.com>
>>
>> fill_bloom_key() allocates memory into bloom_key, we need to clean that
>> up once the key is no longer needed.
>>
>> This fixes the following leak which was found while running t0002-t0099.
>> Although this leak is happening in code being called from a test-helper,
>> the same code is also used in various locations around git, and could
>> presumably happen during normal usage too.
> 
> It does indeed happen: 'git commit-graph write --reachable
> --changed-paths' generates Bloom filters for every commit, with each
> filter containing all paths modified by its associated commit, so it
> leaks a lot of 7 * 4byte hashes.  This patch reduces the memory usage
> of that command:
> 
>                           Max RSS
>                      before      after
>    ---------------------------------------------
>    android-base     1275028k   1006576k   -21.1%
>    chromium         3245144k   3127764k    -3.6%
>    cmssw             793996k    699156k   -12.0%
>    cpython           371584k    343480k    -7.6%
>    elasticsearch     748104k    637936k   -14.7%
>    freebsd-src       819020k    741272k    -9.5%
>    gcc               867412k    730332k   -15.8%
>    gecko-dev        2619112k   2457280k    -6.2%
>    git               252684k    216900k   -14.2%
>    glibc             239000k    222228k    -7.0%
>    go                264132k    251344k    -4.9%
>    homebrew-cask     542188k    480588k   -11.4%
>    homebrew-core     805332k    715848k   -11.1%
>    jdk               417832k    342928k   -17.9%
>    libreoff-core    1257296k   1089980k   -13.3%
>    linux            2033296k   1759712k   -13.5%
>    llvm-project     1067216k    956704k   -10.4%
>    mariadb-srv       695172k    559508k   -19.5%
>    postgres          340132k    317416k    -6.7%
>    rails             325432k    294332k    -9.6%
>    rust              655244k    584904k   -10.7%
>    tensorflow        507308k    480848k    -5.2%
>    webkit           2466812k   2237332k    -9.3%
> 
> Just out of curiosity, I disabled the questionable hardcoded 512 paths
> limit on the size of modified path Bloom filters, and the memory usage
> in the jdk repository sunk by over 55%, from 849520k to 379760k.
> 
> Please feel free to include any of the above data points in the commit
> message.