On Thu, 23 Nov 2006 11:57:29 +0100
Eric Dumazet <[email protected]> wrote:
> On 32bits SMP platforms, 64bits i_size is protected by a seqcount
> (i_size_seqcount).
>
> When i_size is read or written, i_size_seqcount is read/written as well, so it
> make sense to group these two fields together in the same cache line.
>
> Before this patch, accessing i_size needed 3 cache lines (2 for i_size, one
> for i_size_seqcount). After, only one cache line is needed/ (dirtied on a
> i_size change).
I didn't understand that paragraph at all, really, so I took it out.
At present an i_size change will dirty one, two or three cachelines, most
likely one or two.
After your patch an i_size change will dirty one or two cachelines, most
likely one.
yes?
> This patch moves i_size_seqcount next to i_size, and also moves i_version to
> let offsetof(struct inode, i_size) being 0x40 instead of 0x3c (for 32bits
> platforms).
>
> For 64 bits platforms, i_size_seqcount doesnt exist, and the move of a 'long
> i_version' should not introduce a new hole because of padding.
>
> Signed-off-by: Eric Dumazet <[email protected]>
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