linux-kernel - Re: [PATCH] nvmet: Reorder fields in 'struct nvmet

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Message-ID: <f9b06711-6d3c-2271-b2eb-13ab4e8ec040@kernel.dk>
Date:   Thu, 27 Apr 2023 16:51:59 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Chaitanya Kulkarni <kch@...dia.com>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-nvme@...ts.infradead.org
Subject: Re: [PATCH] nvmet: Reorder fields in 'struct nvmet_ns'

On 4/27/23 1:47 PM, Christophe JAILLET wrote:
> Group some variables based on their sizes to reduce holes.
> On x86_64, this shrinks the size of 'struct nvmet_ns' from 520 to 512
> bytes.
> 
> When such a structure is allocated in nvmet_ns_alloc(), because of the way
> memory allocation works, when 520 bytes were requested, 1024 bytes were
> allocated.
> 
> So, on x86_64, this change saves 512 bytes per allocation.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> More aggressive grouping could be done to be more future proof, but the
> way the struct nvmet_ns is written suggest that some fields should be
> kept together. So keep grouping as-is.

I think you did the right thing, that move doesn't matter and it brings
it to pow-of-2 or less and that is really what matters. So looks fine to
me:

Reviewed-by: Jens Axboe <axboe@...nel.dk>

-- 
Jens Axboe