path: root/security
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authorCorrado Zoccolo <>2010-02-27 19:45:39 +0100
committerJens Axboe <>2010-02-28 19:41:25 +0100
commit3dde36ddea3e07dd025c4c1ba47edec91606fec0 (patch)
tree0b8bbdb3fa9a08a3e4c6b0181a7b3325d578b111 /security
parent6fc2de06ef1e691d032aa572478c905b7495a274 (diff)
cfq-iosched: rework seeky detection
Current seeky detection is based on average seek lenght. This is suboptimal, since the average will not distinguish between: * a process doing medium sized seeks * a process doing some sequential requests interleaved with larger seeks and even a medium seek can take lot of time, if the requested sector happens to be behind the disk head in the rotation (50% probability). Therefore, we change the seeky queue detection to work as follows: * each request can be classified as sequential if it is very close to the current head position, i.e. it is likely in the disk cache (disks usually read more data than requested, and put it in cache for subsequent reads). Otherwise, the request is classified as seeky. * an history window of the last 32 requests is kept, storing the classification result. * A queue is marked as seeky if more than 1/8 of the last 32 requests were seeky. This patch fixes a regression reported by Yanmin, on mmap 64k random reads. Reported-by: Yanmin Zhang <> Signed-off-by: Corrado Zoccolo <> Signed-off-by: Jens Axboe <>
Diffstat (limited to 'security')
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