We are missing back pressure channels from uvm to the buf cache. The
buf cache will happily sit on 9000 free pages while uvm churns around
trying to scavenge up one more page.
Fixing this is beyond the scope of a simple diff, but here's something
that seems to help in a lot of the common cases, particularly the pla
deadlock detected spin cycle that people see.
If we're out of memory, kick the buf cache into releasing some
clean pages. The buf cache may eventually find itself sorely in need
of memory and unable to get it, but this is better than nothing. I've
deliberately saved the back pressure until we're already on the about to
die path to minimize regressions. uvm won't steal back memory unless
it absolutely has to.
Index: kern/vfs_bio.c
===================================================================
RCS file: /cvs/src/sys/kern/vfs_bio.c,v
retrieving revision 1.154
diff -u -p -r1.154 vfs_bio.c
--- kern/vfs_bio.c 25 Jan 2014 04:23:31 -0000 1.154
+++ kern/vfs_bio.c 5 Feb 2014 22:08:07 -0000
@@ -305,6 +305,26 @@ bufadjust(int newbufpages)
splx(s);
}
+int
+buf_nukeclean(void)
+{
+ struct buf *bp;
+ int n;
+
+ printf("nuking clean bufs\n");
+ n = 0;
+ while ((bp = TAILQ_FIRST(&bufqueues[BQ_CLEAN])) && n++ < 10) {
+ bremfree(bp);
+ if (bp->b_vp) {
+ RB_REMOVE(buf_rb_bufs,
+ &bp->b_vp->v_bufs_tree, bp);
+ brelvp(bp);
+ }
+ buf_put(bp);
+ }
+ return (n);
+}
+
/*
* Make the buffer cache back off from cachepct.
*/
Index: sys/buf.h
===================================================================
RCS file: /cvs/src/sys/sys/buf.h,v
retrieving revision 1.93
diff -u -p -r1.93 buf.h
--- sys/buf.h 21 Nov 2013 01:16:52 -0000 1.93
+++ sys/buf.h 5 Feb 2014 22:04:09 -0000
@@ -312,6 +312,8 @@ void buf_fix_mapping(struct buf *, vsize
void buf_alloc_pages(struct buf *, vsize_t);
void buf_free_pages(struct buf *);
+int buf_nukeclean(void);
+
void minphys(struct buf *bp);
int physio(void (*strategy)(struct buf *), dev_t dev, int flags,
Index: uvm/uvm_pdaemon.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pdaemon.c,v
retrieving revision 1.64
diff -u -p -r1.64 uvm_pdaemon.c
--- uvm/uvm_pdaemon.c 30 May 2013 16:29:46 -0000 1.64
+++ uvm/uvm_pdaemon.c 5 Feb 2014 22:04:15 -0000
@@ -116,7 +116,7 @@ uvm_wait(const char *wmsg)
* check for page daemon going to sleep (waiting for itself)
*/
- if (curproc == uvm.pagedaemon_proc) {
+ if (curproc == uvm.pagedaemon_proc && buf_nukeclean() == 0) {
/*
* now we have a problem: the pagedaemon wants to go to
* sleep until it frees more memory. but how can it
Index: uvm/uvm_pmemrange.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pmemrange.c,v
retrieving revision 1.36
diff -u -p -r1.36 uvm_pmemrange.c
--- uvm/uvm_pmemrange.c 29 Jan 2013 19:55:48 -0000 1.36
+++ uvm/uvm_pmemrange.c 5 Feb 2014 22:07:37 -0000
@@ -22,6 +22,7 @@
#include <sys/malloc.h>
#include <sys/proc.h> /* XXX for atomic */
#include <sys/kernel.h>
+#include <sys/buf.h>
/*
* 2 trees: addr tree and size tree.
@@ -1883,6 +1884,13 @@ uvm_wait_pla(paddr_t low, paddr_t high,
const char *wmsg = "pmrwait";
if (curproc == uvm.pagedaemon_proc) {
+ uvm_unlock_fpageq();
+ if (buf_nukeclean() != 0) {
+ uvm_lock_fpageq();
+ return 0;
+ }
+ uvm_lock_fpageq();
+
/*
* XXX detect pagedaemon deadlock - see comment in
* uvm_wait(), as this is exactly the same issue.
