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Date: Thu, 21 Feb 2019 21:51:12 -0500 From: "Martin K. Petersen" <martin.petersen@...cle.com> To: Keith Busch <keith.busch@...el.com> Cc: Ric Wheeler <ricwheeler@...il.com>, Dave Chinner <david@...morbit.com>, lsf-pc@...ts.linux-foundation.org, linux-xfs <linux-xfs@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, linux-ext4 <linux-ext4@...r.kernel.org>, linux-btrfs <linux-btrfs@...r.kernel.org>, linux-block@...r.kernel.org Subject: Re: [LSF/MM TOPIC] More async operations for file systems - async discard? Keith, > With respect to fs block sizes, one thing making discards suck is that > many high capacity SSDs' physical page sizes are larger than the fs > block size, and a sub-page discard is worse than doing nothing. That ties into the whole zeroing as a side-effect thing. The devices really need to distinguish between discard-as-a-hint where it is free to ignore anything that's not a whole multiple of whatever the internal granularity is, and the WRITE ZEROES use case where the end result needs to be deterministic. -- Martin K. Petersen Oracle Linux Engineering
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