> > On Thu, May 29, 2014 at 02:42:04PM +0200, Lukáš Czerner wrote: > > > > I wonder what is the performance impact of this change ? Especially > > since we're not longer taking the lock only in unaligned aio/dio > > case but in all cases ? > > Thinking about this some more, this is also going to break parallel > writes, which would be unfortunate. We might want to change this to > using a rw mutex, where writes take a shared lock, and require > fallocate to take an exclusive lock.... ext4 file write is already serialized with inode mutex. So I think the impact of adding another lock will be very very less.. When I run parallel write test of fio to prove it, I can not see the difference on w/wo i_write_mutex. [job1] ioengine=sync buffered=1 rw=write numjobs=100 filename=file1 rw_sequencer=sequential size=10485760000 filesize=104857600 nrfiles=1 openfiles=100 Without i_write_mutex => Run status group 0 (all jobs): WRITE: io=10000MB, aggrb=276869KB/s, minb=2768KB/s, maxb=3530KB/s, mint=29007msec, maxt=36985msec Run status group 0 (all jobs): WRITE: io=10000MB, aggrb=273862KB/s, minb=2738KB/s, maxb=3584KB/s, mint=28566msec, maxt=37391msec Run status group 0 (all jobs): WRITE: io=10000MB, aggrb=271373KB/s, minb=2713KB/s, maxb=3650KB/s, mint=28048msec, maxt=37734msec Run status group 0 (all jobs): WRITE: io=10000MB, aggrb=274906KB/s, minb=2749KB/s, maxb=3554KB/s, mint=28808msec, maxt=37249msec With i_write_mutex patch applied => Run status group 0 (all jobs): WRITE: io=10000MB, aggrb=273672KB/s, minb=2736KB/s, maxb=3498KB/s, mint=29269msec, maxt=37417msec Run status group 0 (all jobs): WRITE: io=10000MB, aggrb=271877KB/s, minb=2718KB/s, maxb=3401KB/s, mint=30101msec, maxt=37664msec Run status group 0 (all jobs): WRITE: io=10000MB, aggrb=272753KB/s, minb=2727KB/s, maxb=3412KB/s, mint=30008msec, maxt=37543msec Run status group 0 (all jobs): WRITE: io=10000MB, aggrb=274508KB/s, minb=2745KB/s, maxb=3267KB/s, mint=31335msec, maxt=37303msec Yes, Right. We can use shared lock to remove a little bit lock contention in ext4 file write. I will share rwsem lock patch.. Could you please revert i_write_mutex patch ? Thanks! > > - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
