Date: Tue, 17 May 2016 09:49:46 +0200 From: Borja Marcos <borjam@sarenet.es> To: Warner Losh <imp@bsdimp.com> Cc: fs@freebsd.org, FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org> Subject: Re: ZFS and NVMe, trim caused stalling Message-ID: <BD7424F9-2968-410D-8146-27496054BCFA@sarenet.es> In-Reply-To: <5E710EA5-C9B0-4521-85F1-3FE87555B0AF@bsdimp.com> References: <5E710EA5-C9B0-4521-85F1-3FE87555B0AF@bsdimp.com>
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> On 05 May 2016, at 16:39, Warner Losh <imp@bsdimp.com> wrote: > >> What do you think? In some cases it’s clear that TRIM can do more harm than good. > > I think it’s best we not overreact. I agree. But with this issue the system is almost unusable for now. > This particular case is cause by the nvd driver, not the Intel P3500 NVME drive. You need > a solution (3): Fix the driver. > > Specifically, ZFS is pushing down a boatload of BIO_DELETE requests. In ata/da land, these > requests are queued up, then collapsed together as much as makes sense (or is possible). > This vastly helps performance (even with the extra sorting that I forced to be in there that I > need to fix before 11). The nvd driver needs to do the same thing. I understand that, but I don’t think it’s a good that ZFS depends blindly on a driver feature such as that. Of course, it’s great to exploit it. I have also noticed that ZFS has a good throttling mechanism for write operations. A similar mechanism should throttle trim requests so that trim requests don’t clog the whole system. > I’d be extremely hesitant to tossing away TRIMs. They are actually quite important for > the FTL in the drive’s firmware to proper manage the NAND wear. More free space always > reduces write amplification. It tends to go as 1 / freespace, so simply dropping them on > the floor should be done with great reluctance. I understand. I was wondering about choosing the lesser between two evils. A 15 minute I/O stall (I deleted 2 TB of data, that’s a lot, but not so unrealistic) or settings trims aside during the peak activity. I see that I was wrong on that, as a throttling mechanism would be more than enough probably, unless the system is close to running out of space. I’ve filed a bug report anyway. And copying to -stable. https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=209571 Thanks! Borja.
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