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: Linus Torvalds Signed-off-by: Wu Fengguang --- fs/read_write.c | 3 +++ include/linux/fs.h | 1 + mm/readahead.c | 5 +++++ 3 files changed, 9 insertions(+) --- linux.orig/mm/readahead.c 2010-02-24 10:44:47.000000000 +0800 +++ linux/mm/readahead.c 2010-02-24 10:44:48.000000000 +0800 @@ -672,6 +672,11 @@ ondemand_readahead(struct address_space if (!offset) { ra_set_pattern(ra, RA_PATTERN_INITIAL); ra->start = offset; + if ((ra->ra_flags & READAHEAD_LSEEK) && req_size <= max) { + ra->size = req_size; + ra->async_size = 0; + goto readit; + } ra->size = get_init_ra_size(req_size, max); ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size; --- linux.orig/fs/read_write.c 2010-02-24 10:44:30.000000000 +0800 +++ linux/fs/read_write.c 2010-02-24 10:44:48.000000000 +0800 @@ -71,6 +71,9 @@ generic_file_llseek_unlocked(struct file file->f_version = 0; } + if (!(file->f_ra.ra_flags & READAHEAD_LSEEK)) + file->f_ra.ra_flags |= READAHEAD_LSEEK; + return offset; } EXPORT_SYMBOL(generic_file_llseek_unlocked); --- linux.orig/include/linux/fs.h 2010-02-24 10:44:45.000000000 +0800 +++ linux/include/linux/fs.h 2010-02-24 10:44:48.000000000 +0800 @@ -899,6 +899,7 @@ struct file_ra_state { #define READAHEAD_MMAP_MISS 0x00000fff /* cache misses for mmap access */ #define READAHEAD_THRASHED 0x10000000 #define READAHEAD_MMAP 0x20000000 +#define READAHEAD_LSEEK 0x40000000 /* be conservative after lseek() */ /* * Which policy makes decision to do the current read-ahead IO? -- 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/