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 | 3 +++ include/linux/fs.h | 1 + mm/readahead.c | 4 ++++ 3 files changed, 8 insertions(+) --- linux-next.orig/mm/readahead.c 2012-01-25 15:57:57.000000000 +0800 +++ linux-next/mm/readahead.c 2012-01-25 15:57:58.000000000 +0800 @@ -485,6 +485,7 @@ unsigned long ra_submit(struct file_ra_s ra->pattern, ra->start, ra->size, ra->async_size, actual); + ra->lseek = 0; ra->for_mmap = 0; ra->for_metadata = 0; return actual; @@ -636,6 +637,8 @@ ondemand_readahead(struct address_space * start of file */ if (!offset) { + if (ra->lseek && req_size < max) + goto random_read; ra->pattern = RA_PATTERN_INITIAL; goto initial_readahead; } @@ -721,6 +724,7 @@ 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 2012-01-25 15:57:46.000000000 +0800 +++ linux-next/fs/read_write.c 2012-01-25 15:57:58.000000000 +0800 @@ -47,6 +47,9 @@ static loff_t lseek_execute(struct file file->f_pos = offset; file->f_version = 0; } + + file->f_ra.lseek = 1; + return offset; } --- linux-next.orig/include/linux/fs.h 2012-01-25 15:57:57.000000000 +0800 +++ linux-next/include/linux/fs.h 2012-01-25 15:57:58.000000000 +0800 @@ -956,6 +956,7 @@ struct file_ra_state { u8 pattern; /* one of RA_PATTERN_* */ unsigned int for_mmap:1; /* readahead for mmap accesses */ unsigned int for_metadata:1; /* readahead for meta data */ + unsigned int lseek:1; /* this read has a leading lseek */ loff_t prev_pos; /* Cache last read() position */ }; -- 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/