linux-kernel - Re: [PATCH RFC 4/8] fs: Introduce FALLOC_FL

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Message-ID: <YylweQAZkIdb5ixo@infradead.org>
Date:   Tue, 20 Sep 2022 00:49:13 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Sarthak Kukreti <sarthakkukreti@...omium.org>
Cc:     dm-devel@...hat.com, linux-block@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Jens Axboe <axboe@...nel.dk>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Bart Van Assche <bvanassche@...gle.com>,
        Daniil Lunev <dlunev@...gle.com>,
        Evan Green <evgreen@...gle.com>,
        Gwendal Grignou <gwendal@...gle.com>
Subject: Re: [PATCH RFC 4/8] fs: Introduce FALLOC_FL_PROVISION

On Thu, Sep 15, 2022 at 09:48:22AM -0700, Sarthak Kukreti wrote:
> From: Sarthak Kukreti <sarthakkukreti@...omium.org>
> 
> FALLOC_FL_PROVISION is a new fallocate() allocation mode that
> sends a hint to (supported) thinly provisioned block devices to
> allocate space for the given range of sectors via REQ_OP_PROVISION.

So, how does that "provisioning" actually work in todays world where
storage is usually doing out of place writes in one or more layers,
including the flash storage everyone is using.  Does it give you one
write?  And unlimited number?  Some undecided number inbetween?  How
is it affected by write zeroes to that range or a discard?