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Subject[PATCH prototype] [3/8] Make readahead max pinned value a sysctl
Date

Previously it was hard coded to 2MB, which seems dubious as systems
are getting more and more memory. With a sysctl it is easier to play
around with it and tune it.

Signed-off-by: Andi Kleen <andi@firstfloor.org>

---
include/linux/mm.h | 2 ++
kernel/sysctl.c | 10 ++++++++++
mm/readahead.c | 14 ++++++++++++--
3 files changed, 24 insertions(+), 2 deletions(-)
Index: linux/mm/readahead.c
===================================================================
--- linux.orig/mm/readahead.c
+++ linux/mm/readahead.c
@@ -17,6 +17,14 @@
#include <linux/pagevec.h>
#include <linux/pagemap.h>

+/*
+ * Max memory pinned during forced readahead.
+ * Should be probably auto scaled with available memory.
+ */
+unsigned ra_max_pinned = 2*1024*1024;
+
+#define MAX_PINNED_CHUNK ra_max_pinned
+
void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
}
@@ -176,7 +184,7 @@ out:
}

/*
- * Chunk the readahead into 2 megabyte units, so that we don't pin too much
+ * Chunk the readahead into MAX_PINNED_CHUNK units, so that we don't pin too much
* memory at once.
*/
int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
@@ -190,7 +198,7 @@ int force_page_cache_readahead(struct ad
while (nr_to_read) {
int err;

- unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE;
+ unsigned long this_chunk = MAX_PINNED_CHUNK / PAGE_CACHE_SIZE;

if (this_chunk > nr_to_read)
this_chunk = nr_to_read;
@@ -229,6 +237,8 @@ int do_page_cache_readahead(struct addre
*/
unsigned long max_sane_readahead(unsigned long nr)
{
+ /* AK: RED-PEN for file cached pages there is no reason
+ to limit ourselves to the current node */
return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE)
+ node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
}
Index: linux/include/linux/mm.h
===================================================================
--- linux.orig/include/linux/mm.h
+++ linux/include/linux/mm.h
@@ -1113,6 +1113,8 @@ void page_cache_async_readahead(struct a

unsigned long max_sane_readahead(unsigned long nr);

+extern unsigned ra_max_pinned;
+
/* Do stack extension */
extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
#ifdef CONFIG_IA64
Index: linux/kernel/sysctl.c
===================================================================
--- linux.orig/kernel/sysctl.c
+++ linux/kernel/sysctl.c
@@ -877,6 +877,16 @@ static struct ctl_table vm_table[] = {
.proc_handler = &proc_dointvec,
},
{
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "ra_max_pinned",
+ .data = &ra_max_pinned,
+ .maxlen = sizeof(ra_max_pinned),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ .strategy = &sysctl_intvec,
+ .extra1 = &zero,
+ },
+ {
.ctl_name = VM_DIRTY_BACKGROUND,
.procname = "dirty_background_ratio",
.data = &dirty_background_ratio,

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