From: Wu Fengguang - Enlarge VM_MAX_READAHEAD to 1024 if new read-ahead code is compiled in. This value is no longer tightly coupled with the thrashing problem, therefore constrained by it. The adaptive read-ahead logic merely takes it as an upper bound, and will not stick to it under memory pressure. - Slightly enlarge minimal/initial read-ahead size on big memory systems. Memory bounty systems are less likely to suffer from thrashing on small read-ahead sizes. A bigger initial value helps the ra_size scaling up progress. Signed-off-by: Wu Fengguang Signed-off-by: Andrew Morton --- include/linux/mm.h | 4 ++++ mm/readahead.c | 19 +++++++++++++++++++ 2 files changed, 23 insertions(+) diff -puN include/linux/mm.h~readahead-min-max-sizes include/linux/mm.h --- a/include/linux/mm.h~readahead-min-max-sizes +++ a/include/linux/mm.h @@ -1007,7 +1007,11 @@ extern int filemap_populate(struct vm_ar int write_one_page(struct page *page, int wait); /* readahead.c */ +#ifdef CONFIG_ADAPTIVE_READAHEAD +#define VM_MAX_READAHEAD 1024 /* kbytes */ +#else #define VM_MAX_READAHEAD 128 /* kbytes */ +#endif #define VM_MIN_READAHEAD 16 /* kbytes (includes current page) */ #define VM_MAX_CACHE_HIT 256 /* max pages in a row in cache before * turning readahead off */ diff -puN mm/readahead.c~readahead-min-max-sizes mm/readahead.c --- a/mm/readahead.c~readahead-min-max-sizes +++ a/mm/readahead.c @@ -783,6 +783,25 @@ out: return nr_pages; } +/* + * ra_min is mainly determined by the size of cache memory. Reasonable? + * + * Table of concrete numbers for 4KB page size: + * inactive + free (MB): 4 8 16 32 64 128 256 512 1024 + * ra_min (KB): 16 16 16 16 20 24 32 48 64 + */ +static inline void get_readahead_bounds(struct file_ra_state *ra, + unsigned long *ra_min, + unsigned long *ra_max) +{ + unsigned long pages; + + pages = max_sane_readahead((1<<30) / PAGE_CACHE_SIZE); + *ra_max = min(min(pages, 0xFFFFUL), ra->ra_pages); + *ra_min = min(min(MIN_RA_PAGES + (pages >> 13), + (128*1024) / PAGE_CACHE_SIZE), *ra_max / 2); +} + #endif /* CONFIG_ADAPTIVE_READAHEAD */ /* _