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/filemap.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index 327910c2400c..1fe962b49f31 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1807,7 +1807,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma, struct file *file, pgoff_t offset) { - unsigned long ra_pages; struct address_space *mapping = file->f_mapping; /* If we don't want any read-ahead, don't bother */ @@ -1836,10 +1835,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma, /* * mmap read-around */ - ra_pages = max_sane_readahead(ra->ra_pages); - ra->start = max_t(long, 0, offset - ra_pages / 2); - ra->size = ra_pages; - ra->async_size = ra_pages / 4; + ra->start = max_t(long, 0, offset - ra->ra_pages / 2); + ra->size = ra->ra_pages; + ra->async_size = ra->ra_pages / 4; ra_submit(ra, mapping, file); } -- cgit v1.2.3