On Sat, Jul 21, 2007 at 11:00:08PM +0200, Peter Zijlstra wrote:
> Scale the default max readahead size with the system memory size.
>
> Signed-off-by: Peter Zijlstra <[EMAIL PROTECTED]>
> ---
> block/ll_rw_blk.c | 2 +-
> include/linux/fs.h | 1 +
> mm/readahead.c | 32 ++++++++++++++++++++++++++++++++
> 3 files changed, 34 insertions(+), 1 deletion(-)
>
> Index: linux-2.6/block/ll_rw_blk.c
> ===================================================================
> --- linux-2.6.orig/block/ll_rw_blk.c
> +++ linux-2.6/block/ll_rw_blk.c
> @@ -208,7 +208,7 @@ void blk_queue_make_request(request_queu
> blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
> blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
> q->make_request_fn = mfn;
> - q->backing_dev_info.ra_pages = (VM_MAX_READAHEAD * 1024) /
> PAGE_CACHE_SIZE;
> + bdi_ra_init(&q->backing_dev_info);
fs/fuse/inode.c has another line to be converted.
> q->backing_dev_info.state = 0;
> q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
> blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
> Index: linux-2.6/include/linux/fs.h
> ===================================================================
> --- linux-2.6.orig/include/linux/fs.h
> +++ linux-2.6/include/linux/fs.h
> @@ -1696,6 +1696,7 @@ extern long do_splice_direct(struct file
>
> extern void
> file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);
> +extern void bdi_ra_init(struct backing_dev_info *bdi);
> extern loff_t no_llseek(struct file *file, loff_t offset, int origin);
> extern loff_t generic_file_llseek(struct file *file, loff_t offset, int
> origin);
> extern loff_t remote_llseek(struct file *file, loff_t offset, int origin);
> Index: linux-2.6/mm/readahead.c
> ===================================================================
> --- linux-2.6.orig/mm/readahead.c
> +++ linux-2.6/mm/readahead.c
> @@ -42,6 +42,38 @@ file_ra_state_init(struct file_ra_state
> }
> EXPORT_SYMBOL_GPL(file_ra_state_init);
>
> +static unsigned long ra_pages;
> +
> +static __init int readahead_init(void)
> +{
> + /*
> + * Scale the max readahead window with system memory
> + *
> + * 64M: 128K
> + * 128M: 180K
> + * 256M: 256K
> + * 512M: 360K
> + * 1G: 512K
> + * 2G: 724K
> + * 4G: 1024K
> + * 8G: 1448K
> + * 16G: 2048K
> + */
> + ra_pages = int_sqrt(totalram_pages/16);
> + if (ra_pages > (2 << (20 - PAGE_SHIFT)))
> + ra_pages = 2 << (20 - PAGE_SHIFT);
We can elaborate on the numbers ;)
How about the following rules?
- limit it under 1MB: we have to consider latencies
- make them alignment-friendly, i.e. 128K, 256K, 512K, 1M.
My original plan is to simply do the following:
- #define VM_MAX_READAHEAD 128 /* kbytes */
+ #define VM_MAX_READAHEAD 512 /* kbytes */
I'd like to post some numbers to back-up the discussion:
readahead readahead
size miss
128K 38%
512K 45%
1024K 49%
The numbers are measured on a fresh booted KDE desktop.
The majority misses come from the larger mmap read-arounds.
Sequential readahead hits are pretty high and not quite affected by
the readahead size, thanks to its size ramp-up process.
> +
> + return 0;
> +}
> +
> +subsys_initcall(readahead_init);
Remove the global ra_pages and fold readahead_init() into bdi_ra_init()?
bdi_ra_init will only be called several times I guess.
> +
> +void bdi_ra_init(struct backing_dev_info *bdi)
> +{
> + bdi->ra_pages = ra_pages;
> +}
> +EXPORT_SYMBOL(bdi_ra_init);
-
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