Reserve a second segment for the page daemon.

This ensures uvm_swap_io() can succeeds even in OOM situations because two
uvm_pagermapin() allocations, requiring a segment each, are needed to bounce
or encrypt a swap cluster.

ok beck@, kettenis@

diff --git a/sys/uvm/uvm_pager.c b/sys/uvm/uvm_pager.c
index 829da96..4f8a96c 100644 (file)
--- a/sys/uvm/uvm_pager.c
+++ b/sys/uvm/uvm_pager.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: uvm_pager.c,v 1.80 2022/06/28 12:10:37 mpi Exp $      */
+/*     $OpenBSD: uvm_pager.c,v 1.81 2022/06/28 19:07:40 mpi Exp $      */
 /*     $NetBSD: uvm_pager.c,v 1.36 2000/11/27 18:26:41 chs Exp $       */
 
 /*
@@ -58,8 +58,8 @@ const struct uvm_pagerops *uvmpagerops[] = {
  * The number of uvm_pseg instances is dynamic using an array segs.
  * At most UVM_PSEG_COUNT instances can exist.
  *
- * psegs[0] always exists (so that the pager can always map in pages).
- * psegs[0] element 0 is always reserved for the pagedaemon.
+ * psegs[0/1] always exist (so that the pager can always map in pages).
+ * psegs[0/1] element 0 are always reserved for the pagedaemon.
  *
  * Any other pseg is automatically created when no space is available
  * and automatically destroyed when it is no longer in use.
@@ -93,6 +93,7 @@ uvm_pager_init(void)
 
        /* init pager map */
        uvm_pseg_init(&psegs[0]);
+       uvm_pseg_init(&psegs[1]);
        mtx_init(&uvm_pseg_lck, IPL_VM);
 
        /* init ASYNC I/O queue */
@@ -168,9 +169,10 @@ pager_seg_restart:
                                goto pager_seg_fail;
                }
 
-               /* Keep index 0 reserved for pagedaemon. */
-               if (pseg == &psegs[0] && curproc != uvm.pagedaemon_proc)
-                       i = 1;
+               /* Keep indexes 0,1 reserved for pagedaemon. */
+               if ((pseg == &psegs[0] || pseg == &psegs[1]) &&
+                   (curproc != uvm.pagedaemon_proc))
+                       i = 2;
                else
                        i = 0;
 
@@ -229,7 +231,7 @@ uvm_pseg_release(vaddr_t segaddr)
        pseg->use &= ~(1 << id);
        wakeup(&psegs);
 
-       if (pseg != &psegs[0] && UVM_PSEG_EMPTY(pseg)) {
+       if ((pseg != &psegs[0] && pseg != &psegs[1]) && UVM_PSEG_EMPTY(pseg)) {
                va = pseg->start;
                pseg->start = 0;
        }