Use the VM_ALLOC_INTERRUPT for the page requests when allocating memory

for the bio for swapout write. It allows the page allocator to drain
free page list deeper. As result, a deadlock where pageout deamon sleeps
waiting for bio to be allocated for swapout is no more reproducable in
practice.

Alan said that M_USE_RESERVE shall be ressurrected and used there, but
until this is implemented, M_NOWAIT does exactly what is needed.

Tested by:	pho, kris
Reviewed by:	alc
No objections from:	phk
MFC after:	2 weeks (RELENG_7 only)

1 files changed, 5 insertions, 7 deletions

diff --git a/sys/vm/swap_pager.c b/sys/vm/swap_pager.c
index eb910f7..39af009 100644
--- a/sys/vm/swap_pager.c
+++ b/sys/vm/swap_pager.c
@@ -2339,19 +2339,17 @@ swapgeom_strategy(struct buf *bp, struct swdevt *sp)
 		bufdone(bp);
 		return;
 	}
-	bio = g_alloc_bio();
-#if 0
-	/*
-	 * XXX: We shouldn't really sleep here when we run out of buffers
-	 * XXX: but the alternative is worse right now.
-	 */
+	if (bp->b_iocmd == BIO_WRITE)
+		bio = g_new_bio();
+	else
+		bio = g_alloc_bio();
 	if (bio == NULL) {
 		bp->b_error = ENOMEM;
 		bp->b_ioflags |= BIO_ERROR;
 		bufdone(bp);
 		return;
 	}
-#endif
+
 	bio->bio_caller2 = bp;
 	bio->bio_cmd = bp->b_iocmd;
 	bio->bio_data = bp->b_data;