Some applications (eg. blkid, id3tool etc.) seek around the file to get information. For example, blkid does seek to 0 read 1024 seek to 1536 read 16384 The start-of-file readahead heuristic is wrong for them, whose access pattern can be identified by lseek() calls. So test-and-set a READAHEAD_LSEEK flag on lseek() and don't do start-of-file readahead on seeing it. Proposed by Linus. Acked-by: Rik van Riel Acked-by: Linus Torvalds Signed-off-by: Wu Fengguang --- fs/read_write.c | 4 ++++ include/linux/fs.h | 1 + mm/readahead.c | 3 +++ 3 files changed, 8 insertions(+) --- linux-next.orig/mm/readahead.c 2011-11-20 22:02:01.000000000 +0800 +++ linux-next/mm/readahead.c 2011-11-20 22:02:03.000000000 +0800 @@ -629,6 +629,8 @@ ondemand_readahead(struct address_space * start of file */ if (!offset) { + if ((ra->ra_flags & READAHEAD_LSEEK) && req_size < max) + goto random_read; ra_set_pattern(ra, RA_PATTERN_INITIAL); goto initial_readahead; } @@ -707,6 +709,7 @@ ondemand_readahead(struct address_space if (try_context_readahead(mapping, ra, offset, req_size, max)) goto readit; +random_read: /* * standalone, small random read */ --- linux-next.orig/fs/read_write.c 2011-11-20 22:02:01.000000000 +0800 +++ linux-next/fs/read_write.c 2011-11-20 22:02:03.000000000 +0800 @@ -47,6 +47,10 @@ static loff_t lseek_execute(struct file file->f_pos = offset; file->f_version = 0; } + + if (!(file->f_ra.ra_flags & READAHEAD_LSEEK)) + file->f_ra.ra_flags |= READAHEAD_LSEEK; + return offset; } --- linux-next.orig/include/linux/fs.h 2011-11-20 22:02:01.000000000 +0800 +++ linux-next/include/linux/fs.h 2011-11-20 22:02:03.000000000 +0800 @@ -952,6 +952,7 @@ struct file_ra_state { /* ra_flags bits */ #define READAHEAD_MMAP_MISS 0x000003ff /* cache misses for mmap access */ #define READAHEAD_MMAP 0x00010000 +#define READAHEAD_LSEEK 0x00020000 /* be conservative after lseek() */ #define READAHEAD_PATTERN_SHIFT 28 #define READAHEAD_PATTERN 0xf0000000 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/