On Sat, 2007-07-21 at 16:29 -0400, Eric St-Laurent wrote:
> On Sat, 2007-21-07 at 23:00 +0200, Peter Zijlstra wrote:
> > plain text document attachment (readahead-useonce.patch)
> > Use the read-ahead code to provide hints to page reclaim.
> >
> > This patch has the potential to solve the streaming-IO trashes my
> > desktop problem.
> >
> > It tries to aggressively reclaim pages that were loaded in a strong
> > sequential pattern and have been consumed. Thereby limiting the damage
> > to the current resident set.
> >
> > Signed-off-by: Peter Zijlstra <[email protected]>
>
> With the fadvise change, it looks like the right solution to me.
>
> The patches are for which kernel? They doesn't apply cleanly to
> 2.6.22.1.
They are against git of a few hours ago and the latest readahead patches
from Wu (which don't apply cleanly either, but the rejects are trivial).
> It would be useful to have a temporary /proc tunable to enable/disable
> the heuristic to help test the effects.
Right, I had such a patch somewhere,.. won't apply cleanly but should be
obvious..
---
kernel/sysctl.c | 9 +++++++++
mm/readahead.c | 6 ++++--
2 files changed, 13 insertions(+), 2 deletions(-)
Index: linux-2.6/kernel/sysctl.c
===================================================================
--- linux-2.6.orig/kernel/sysctl.c
+++ linux-2.6/kernel/sysctl.c
@@ -168,6 +168,7 @@ extern int dirty_ratio_handler(ctl_table
extern int prove_locking;
extern int lock_stat;
+extern int sysctl_dropbehind;
/* The default sysctl tables: */
@@ -1075,6 +1076,14 @@ static ctl_table vm_table[] = {
.extra1 = &zero,
},
#endif
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "drop_behind",
+ .data = &sysctl_dropbehind,
+ .maxlen = sizeof(sysctl_dropbehind),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
/*
* NOTE: do not add new entries to this table unless you have read
* Documentation/sysctl/ctl_unnumbered.txt
Index: linux-2.6/mm/readahead.c
===================================================================
--- linux-2.6.orig/mm/readahead.c
+++ linux-2.6/mm/readahead.c
@@ -429,6 +429,8 @@ void page_cache_sync_readahead(struct ad
}
EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
+int sysctl_dropbehind = 2;
+
/**
* page_cache_async_readahead - file readahead for marked pages
* @mapping: address_space which holds the pagecache and I/O vectors
@@ -473,7 +475,7 @@ 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) {
+ if (sysctl_dropbehind && ra->size == ra->ra_pages) {
unsigned long demote_idx = offset - min(offset, ra->size);
read_lock_irq(&mapping->tree_lock);
@@ -489,7 +491,7 @@ page_cache_async_readahead(struct addres
* users. We should not take away somebody else's
* pages, so do not drop behind beyond this point.
*/
- if (PageActive(page))
+ if (sysctl_dropbehind > 1 && PageActive(page))
break;
lru_demote(page);
-
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