[PATCH 2/2] dim: Try to gc the rr-cache

[Jani Nikula]

On Thu, 13 Jul 2017, Sean Paul <seanpaul at chromium.org> wrote:
> On Wed, Jul 12, 2017 at 02:12:24PM +0200, Daniel Vetter wrote:
>> The problem is that we have a distributed cache - every committer has
>> a copy. Which means even just a slight clock skew will make sure that
>> a naive gc algorithm results in lots of thrashing around.
>> 
>> To fix this add a huge hysteresis: Only add files newer than 1 day,
>> and only remove them when older than 60 days. As long as people have
>> reasonable accurate clocks on their machines this should work.
>> 
>> A different problem is that we can't use filesystem timestamps (and
>> hence can't use git rerere gc): When someone comes back from vacations
>> and updates git rerere, all the files will have current timestamps,
>> even when they've been pushed out weeks ago. To fix that, use the git
>> log to judge old files to remove. Also, remove old files before adding
>> new ones, to avoid confusion.
>> 
>> Also, we need to teach the cp -r to preserve timestamps, otherwise
>> this won't work.
>> 
>> v2: Use git log to remove old files.
>> 
>> v3: Remove the debug uncommenting (Sean).
>> 
>> v4: Split out code movement and explain better what's going on (Jani).
>
> Yeah, much easier to digest with the split.
>
> Reviewed-by: Sean Paul <seanpaul at chromium.org>

I'll trust that and hope for the best. ;)

BR,
Jani.


>
>> 
>> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
>> ---
>>  dim | 10 ++++++++--
>>  1 file changed, 8 insertions(+), 2 deletions(-)
>> 
>> diff --git a/dim b/dim
>> index b788edd29653..79d616cbf354 100755
>> --- a/dim
>> +++ b/dim
>> @@ -513,9 +513,15 @@ function commit_rerere_cache
>>  
>>  		git pull >& /dev/null
>>  		rm $(rr_cache_dir)/rr-cache -Rf &> /dev/null || true
>> -		cp $(rr_cache_dir)/* rr-cache -r
>> +		cp $(rr_cache_dir)/* rr-cache -r --preserve=timestamps
>>  		git add ./*.patch >& /dev/null || true
>> -		git add rr-cache/* > /dev/null
>> +		for file  in $(git ls-files); do
>> +			if ! git log --since="60 days ago" --name-only -- $file | grep $file &> /dev/null; then
>> +				git rm $file &> /dev/null
>> +				echo deleting $file
>> +			fi
>> +		done
>> +		find rr-cache/ -ctime -1 -type f -print0 | xargs -0 git add > /dev/null
>>  		git rm rr-cache/rr-cache &> /dev/null || true
>>  		if git commit -m "$time: $integration_branch rerere cache update" >& /dev/null; then
>>  			echo -n "New commit. "
>> -- 
>> 2.13.2
>> 
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-- 
Jani Nikula, Intel Open Source Technology Center