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Date:   Thu, 21 Feb 2019 21:51:12 -0500
From:   "Martin K. Petersen" <>
To:     Keith Busch <>
Cc:     Ric Wheeler <>,
        Dave Chinner <>,,
        linux-xfs <>,
        linux-fsdevel <>,
        linux-ext4 <>,
        linux-btrfs <>,
Subject: Re: [LSF/MM TOPIC] More async operations for file systems - async discard?


> 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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