currently drop behind is controlled by a heuristic:
ra->size == ra->ra_pages
provide some fadvise() control:
POSIX_FADV_NORMAL - heuristic
POSIX_FADV_RANDOM - always disable drop behind
POSIX_FADV_SEQUENTIAL - always enable drop behind
Signed-off-by: Peter Zijlstra <[email protected]>
---
include/linux/fs.h | 7 +++++++
mm/fadvise.c | 5 +++++
mm/readahead.c | 4 +++-
3 files changed, 15 insertions(+), 1 deletion(-)
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h
@@ -705,8 +705,15 @@ struct file_ra_state {
unsigned int ra_pages; /* Maximum readahead window */
int mmap_miss; /* Cache miss stat for mmap accesses */
loff_t prev_pos; /* Cache last read() position */
+ unsigned int flags; /* readahead flags */
};
+#define F_RA_DROP_BEHIND_NEVER 1
+#define F_RA_DROP_BEHIND_ALWAYS 2
+
+#define F_RA_DROP_BEHIND_MASK \
+ (F_RA_DROP_BEHIND_NEVER|F_RA_DROP_BEHIND_ALWAYS)
+
/*
* Check if @index falls in the readahead windows.
*/
Index: linux-2.6/mm/fadvise.c
===================================================================
--- linux-2.6.orig/mm/fadvise.c
+++ linux-2.6/mm/fadvise.c
@@ -65,12 +65,17 @@ asmlinkage long sys_fadvise64_64(int fd,
switch (advice) {
case POSIX_FADV_NORMAL:
file->f_ra.ra_pages = bdi->ra_pages;
+ file->f_ra.flags &= ~F_RA_DROP_BEHIND_MASK;
break;
case POSIX_FADV_RANDOM:
file->f_ra.ra_pages = 0;
+ file->f_ra.flags &= ~F_RA_DROP_BEHIND_MASK;
+ file->f_ra.flags |= F_RA_DROP_BEHIND_NEVER;
break;
case POSIX_FADV_SEQUENTIAL:
file->f_ra.ra_pages = bdi->ra_pages * 2;
+ file->f_ra.flags &= ~F_RA_DROP_BEHIND_MASK;
+ file->f_ra.flags |= F_RA_DROP_BEHIND_ALWAYS;
break;
case POSIX_FADV_WILLNEED:
if (!mapping->a_ops->readpage) {
Index: linux-2.6/mm/readahead.c
===================================================================
--- linux-2.6.orig/mm/readahead.c
+++ linux-2.6/mm/readahead.c
@@ -485,7 +485,9 @@ page_cache_async_readahead(struct addres
* hint that there is sequential IO, which implies that the pages that
* have been used thus far can be reclaimed
*/
- if (ra->size == ra->ra_pages) do {
+ if (!(ra->flags & F_RA_DROP_BEHIND_NEVER) &&
+ ((ra->flags & F_RA_DROP_BEHIND_ALWAYS) ||
+ ra->size == ra->ra_pages)) do {
nr_pages = find_get_pages(mapping,
demote_idx, ARRAY_SIZE(pages), pages);
--
-
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