linux-kernel - Re: [RFC 4/8] shmem: add helpers to get block size

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Message-ID: <ZEMTB4uKgKJKQRHo@casper.infradead.org>
Date:   Fri, 21 Apr 2023 23:49:43 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     hughd@...gle.com, akpm@...ux-foundation.org, brauner@...nel.org,
        djwong@...nel.org, p.raghav@...sung.com, da.gomez@...sung.com,
        a.manzanares@...sung.com, dave@...olabs.net, yosryahmed@...gle.com,
        keescook@...omium.org, hare@...e.de, kbusch@...nel.org,
        patches@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 4/8] shmem: add helpers to get block size

On Fri, Apr 21, 2023 at 02:43:56PM -0700, Luis Chamberlain wrote:
>  struct shmem_sb_info {
> +#ifdef CONFIG_TMPFS
> +	u64 blocksize;
> +#endif

u64?  You're planning on supporting a blocksize larger than 2GB?

I would store block_order (in an unsigned char) and then you can avoid
the call to ffs(), at the expense of doing 1UL << sbi->block_order;