On Fri, 23 Jul 2010, Ted Ts'o wrote: > On Wed, Jul 07, 2010 at 09:53:30AM +0200, Lukas Czerner wrote: > > > > Hi all, > > > > since my last post I have done some more testing with various SSD's and the > > trend is clear. Trim performance is getting better and the performance loss > > without trim is getting lower. So I have decided to abandon the initial idea > > to track free blocks within some internal data structure - it takes time and > > memory. > > Do you have some numbers about how bad trim actually might be on > various devices? I can imagine some devices where it might be better > (for wear levelling and better write endurance if nothing else) where > it's better to do the trim right away instead of batching things. Hi, Yes, I have those numbers. http://people.redhat.com/jmoyer/discard/ext4_batched_discard/ext4_discard.html This page presents my test results on three different devices. I have tested the current ext4 discard implementation (do the trim right away). However, one tested device is still not on that page. With this (Vendor4) device I have got only about 1.83% performance loss, which is very good. http://people.redhat.com/jmoyer/discard/ext4_batched_discard/ext4_ioctltrim.html This page provides test results with my batched discard implementation. Take those numbers with discretion, because the patch still does not involve journaling and I have tested the "worst case" scenario, which involves issuing FITRIM in endless loop without any sleep. Generally the FITRIM ioctl can take from 2 seconds on fast devices to several (2-4) minutes on very slow devices, or under heavy load. > > So what I'm thinking about doing is keeping the "discard" mount option > to mean non-batched discard. If you want to use the explicit FITRIM > ioctl, I don't think we need to test to see if the dicard mount option > is set; if the user issues the ioctl, then we should do the batched > discard, and if we don't trust the user to do that, then well, the > ioctl should be restricted to privileged users only --- especially if > it could take up to a minute. I agree. > > - Ted > Thanks. -Lukas -- 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
