From: Andrew Morton Date: Sat, 5 Aug 2006 19:14:25 +0000 (-0700) Subject: [PATCH] fadvise() make POSIX_FADV_NOREUSE a no-op X-Git-Tag: v2.6.18-rc4~27 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=60c371bc753495f36d3a71338b46030f7fffce3b;p=linux-2.6-omap-h63xx.git [PATCH] fadvise() make POSIX_FADV_NOREUSE a no-op The POSIX_FADV_NOREUSE hint means "the application will use this range of the file a single time". It seems to be intended that the implementation will use this hint to perform drop-behind of that part of the file when the application gets around to reading or writing it. However for reasons which aren't obvious (or sane?) I mapped POSIX_FADV_NOREUSE onto POSIX_FADV_WILLNEED. ie: it does readahead. That's daft. So for now, make POSIX_FADV_NOREUSE a no-op. This is a non-back-compatible change. If someone was using POSIX_FADV_NOREUSE to perform readahead, they lose. The likelihood is low. If/when we later implement POSIX_FADV_NOREUSE things will get interesting - to do it fully we'll need to maintain file offset/length ranges and peform all sorts of complex tricks, and managing the lifetime of those ranges' data structures will be interesting.. A sensible implementation would probably ignore the file range and would simply mark the entire file as needing some form of drop-behind treatment. Cc: Michael Kerrisk Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/fadvise.c b/mm/fadvise.c index 60a5d55e51d..168c78a121b 100644 --- a/mm/fadvise.c +++ b/mm/fadvise.c @@ -73,7 +73,6 @@ asmlinkage long sys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice) file->f_ra.ra_pages = bdi->ra_pages * 2; break; case POSIX_FADV_WILLNEED: - case POSIX_FADV_NOREUSE: if (!mapping->a_ops->readpage) { ret = -EINVAL; break; @@ -94,6 +93,8 @@ asmlinkage long sys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice) if (ret > 0) ret = 0; break; + case POSIX_FADV_NOREUSE: + break; case POSIX_FADV_DONTNEED: if (!bdi_write_congested(mapping->backing_dev_info)) filemap_flush(mapping);