On Fri 10-01-14 00:54:50, Raghavendra K T wrote:
> We limit the number of readahead pages to 4k.
>
> max_sane_readahead returns zero on the cpu having no local memory
> node. Fix that by returning a sanitized number of pages viz.,
> minimum of (requested pages, 4k, number of local free pages)
>
> Result:
> fadvise experiment with FADV_WILLNEED on a x240 machine with 1GB testfile
> 32GB* 4G RAM numa machine ( 12 iterations) yielded
>
> kernel Avg Stddev
> base 7.264 0.56%
> patched 7.285 1.14%
OK, looks good to me. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
>
> Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
> ---
> mm/readahead.c | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> V4: incorporated 16MB limit suggested by Linus for readahead and
> fixed transitioning to large readahead anomaly pointed by Andrew Morton with
> Honza's suggestion.
>
> Test results shows no significant overhead with the current changes.
>
> (Do I have to break patches into two??)
>
> Suggestions/Comments please let me know.
>
> diff --git a/mm/readahead.c b/mm/readahead.c
> index 7cdbb44..2f561a0 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -237,14 +237,30 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
> return ret;
> }
>
> +#define MAX_REMOTE_READAHEAD 4096UL
> /*
> * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
> * sensible upper limit.
> */
> unsigned long max_sane_readahead(unsigned long nr)
> {
> - return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE)
> - + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
> + unsigned long local_free_page;
> + unsigned long sane_nr;
> + int nid;
> +
> + nid = numa_node_id();
> + sane_nr = min(nr, MAX_REMOTE_READAHEAD);
> +
> + local_free_page = node_page_state(nid, NR_INACTIVE_FILE)
> + + node_page_state(nid, NR_FREE_PAGES);
> +
> + /*
> + * Readahead onto remote memory is better than no readahead when local
> + * numa node does not have memory. We sanitize readahead size depending
> + * on free memory in the local node but limiting to 4k pages.
> + */
> + return node_present_pages(nid) ?
> + min(sane_nr, local_free_page / 2) : sane_nr;
> }
>
> /*
> --
> 1.7.11.7
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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