From 600e19afc5f8a6c18ea49cee9511c5797db02391 Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Thu, 5 Nov 2015 18:47:08 -0800 Subject: mm: use only per-device readahead limit Maximal readahead size is limited now by two values: 1) by global 2Mb constant (MAX_READAHEAD in max_sane_readahead()) 2) by configurable per-device value* (bdi->ra_pages) There are devices, which require custom readahead limit. For instance, for RAIDs it's calculated as number of devices multiplied by chunk size times 2. Readahead size can never be larger than bdi->ra_pages * 2 value (POSIX_FADV_SEQUNTIAL doubles readahead size). If so, why do we need two limits? I suggest to completely remove this max_sane_readahead() stuff and use per-device readahead limit everywhere. Also, using right readahead size for RAID disks can significantly increase i/o performance: before: dd if=/dev/md2 of=/dev/null bs=100M count=100 100+0 records in 100+0 records out 10485760000 bytes (10 GB) copied, 12.9741 s, 808 MB/s after: $ dd if=/dev/md2 of=/dev/null bs=100M count=100 100+0 records in 100+0 records out 10485760000 bytes (10 GB) copied, 8.91317 s, 1.2 GB/s (It's an 8-disks RAID5 storage). This patch doesn't change sys_readahead and madvise(MADV_WILLNEED) behavior introduced by 6d2be915e589b58 ("mm/readahead.c: fix readahead failure for memoryless NUMA nodes and limit readahead pages"). Signed-off-by: Roman Gushchin Cc: Raghavendra K T Cc: Jan Kara Cc: Wu Fengguang Cc: David Rientjes Cc: onstantin Khlebnikov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/readahead.c | 14 ++------------ 1 file changed, 2 insertions(+), 12 deletions(-) (limited to 'mm/readahead.c') diff --git a/mm/readahead.c b/mm/readahead.c index 24682f6f4cfd..998ad592f408 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -213,7 +213,7 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp, if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) return -EINVAL; - nr_to_read = max_sane_readahead(nr_to_read); + nr_to_read = min(nr_to_read, inode_to_bdi(mapping->host)->ra_pages); while (nr_to_read) { int err; @@ -232,16 +232,6 @@ 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, MAX_READAHEAD); -} - /* * Set the initial window size, round to next power of 2 and square * for small size, x 4 for medium, and x 2 for large @@ -380,7 +370,7 @@ ondemand_readahead(struct address_space *mapping, bool hit_readahead_marker, pgoff_t offset, unsigned long req_size) { - unsigned long max = max_sane_readahead(ra->ra_pages); + unsigned long max = ra->ra_pages; pgoff_t prev_offset; /* -- cgit v1.2.3-70-g09d2