On Tue 18-02-14 12:55:38, Raghavendra K T wrote:
> Currently max_sane_readahead() returns zero on the cpu having no local memory
> node
> which leads to readahead failure. Fix the readahead failure by returning
> minimum of (requested pages, 512). Users running application on a memory-less
> cpu
> which needs readahead such as streaming application see considerable boost in
> the
> performance.
>
> Result:
> fadvise experiment with FADV_WILLNEED on a PPC machine having memoryless CPU
> with 1GB testfile ( 12 iterations) yielded around 46.66% improvement.
>
> fadvise experiment with FADV_WILLNEED on a x240 machine with 1GB testfile
> 32GB* 4G RAM numa machine ( 12 iterations) showed no impact on the normal
> NUMA cases w/ patch.
Can you try one more thing please? Compare startup time of some big
executable (Firefox or LibreOffice come to my mind) for the patched and
normal kernel on a machine which wasn't hit by this NUMA issue. And don't
forget to do "echo 3 >/proc/sys/vm/drop_caches" before each test to flush
the caches. If this doesn't show significant differences, I'm OK with the
patch.
Honza
> Kernel Avg Stddev
> base 7.4975 3.92%
> patched 7.4174 3.26%
>
> Suggested-by: Linus Torvalds <torva...@linux-foundation.org>
> [Andrew: making return value PAGE_SIZE independent]
> Signed-off-by: Raghavendra K T <raghavendra...@linux.vnet.ibm.com>
> ---
> I would like to thank Honza, David for their valuable suggestions and
> patiently reviewing the patches.
>
> Changes in V6:
> - Just limit the readahead to 2MB on 4k pages system as suggested by Linus.
> and make it independent of PAGE_SIZE.
>
> Changes in V5:
> - Drop the 4k limit for normal readahead. (Jan Kara)
>
> Changes in V4:
> - Check for total node memory to decide whether we don't
> have local memory (jan Kara)
> - Add 4k page limit on readahead for normal and remote readahead (Linus)
> (Linus suggestion was 16MB limit).
>
> Changes in V3:
> - Drop iterating over numa nodes that calculates total free pages (Linus)
>
> Agree that we do not have control on allocation for readahead on a
> particular numa node and hence for remote readahead we can not further
> sanitize based on potential free pages of that node. and also we do
> not want to itererate through all nodes to find total free pages.
>
> Suggestions and comments welcome
> mm/readahead.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/readahead.c b/mm/readahead.c
> index 0de2360..1fa0d6f 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -233,14 +233,14 @@ int force_page_cache_readahead(struct address_space
> *mapping, struct file *filp,
> return 0;
> }
>
> +#define MAX_READAHEAD ((512*4096)/PAGE_CACHE_SIZE)
> /*
> * 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);
> + return min(nr, MAX_READAHEAD);
> }
>
> /*
> --
> 1.7.11.7
>
--
Jan Kara <j...@suse.cz>
SUSE Labs, CR
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