Re: [PATCH] avoid atomic op on page free

[Nick Piggin <nickpiggin@yahoo.com.au>]

Benjamin LaHaise wrote:

>Hello Andrew et al,
>
>The patch below adds a fast path that avoids the atomic dec and test 
>operation and spinlock acquire/release on page free.  This is especially 
>important to the network stack which uses put_page() to free user 
>buffers.  Removing these atomic ops helps improve netperf on the P4 
>from ~8126Mbit/s to ~8199Mbit/s (although that number fluctuates quite a 
>bit with some runs getting 8243Mbit/s).  There are probably better 
>workloads to see an improvement from this on, but removing 3 atomics and 
>an irq save/restore is good.
>
>		-ben
>

You can't do this because you can't test PageLRU like that.

Have a look in the lkml archives a few months back, where I proposed
a way to do this for __free_pages(). You can't do it for put_page.

BTW I have quite a large backlog of patches in -mm which should end
up avoiding an atomic or two around these parts.

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