linux-kernel - Re: [PATCH 0/5] optimize some data structure in nvme

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Message-ID: <012a86ad-933a-2948-29d3-764346afbd6e@grimberg.me>
Date:   Mon, 1 May 2023 16:57:09 +0300
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>, hch@....de,
        kch@...dia.com
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 0/5] optimize some data structure in nvme


> This serie is a proposal to slighly optimize the memory needed for some
> structures used in nvme.
> 
> This follows the discussion in [1].
> 
> Honnestly, I'm not convinced that this serie really brings semething.
> Because of the way memory alocation works, and its over-allocation to try to
> avoid memory fragmentation, some limited gains are most of the time useless.
> 
> It could still help:
>     - many holes in structure can, at some point, have its size reach a threshold
>       (this is specially true if such structures are allocated with kcalloc() or
>       kmalloc_array())
>     - it can save some space in some other structures if embedded in them
>     - it can save a few cycles if the structure is memcpy()'ed or zeroed, for
>       example
>     - can reduce cache usage
> 
> With that in mind, patch 3 is a win, patch 4 is likely a win, the other ones are
> much more theorical.
> 
> The changes are really limited, so even if the gain is marginal, maybe it still
> makes sense to merge them.

Don't see why not, given they make do the structures smaller.

Reviewed-by: Sagi Grimberg <sagi@...mberg.me>