Re: kern/40027 (pagedaemon loops on memory shortage)

[Andrew Doran <ad%NetBSD.org@localhost>]

The following reply was made to PR kern/40027; it has been noted by GNATS.

From: Andrew Doran <ad%NetBSD.org@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/40027 (pagedaemon loops on memory shortage)
Date: Wed, 3 Dec 2008 14:04:57 +0000

 With this patch against -current and the test program, a dual CPU machine
 with 128MB RAM stalls during heavy paging activity, but eventually the
 memory hog process is killed and it recovers.
 
 Memory: 3728K Act, 2156K Inact, 500K Wired, 4484K Exec, 124K File, 95M Free
 
 Andrew
 
 Index: uvm_km.c
 ===================================================================
 RCS file: /cvsroot/src/sys/uvm/uvm_km.c,v
 retrieving revision 1.102
 diff -u -p -r1.102 uvm_km.c
 --- uvm_km.c   1 Dec 2008 10:54:57 -0000       1.102
 +++ uvm_km.c   3 Dec 2008 13:53:34 -0000
 @@ -589,7 +589,9 @@ uvm_km_alloc(struct vm_map *map, vsize_t
        loopva = kva;
        loopsize = size;
  
 -      pgaflags = UVM_PGA_USERESERVE;
 +      pgaflags = 0;
 +      if (flags & UVM_KMF_NOWAIT)
 +              pgaflags |= UVM_PGA_USERESERVE;
        if (flags & UVM_KMF_ZERO)
                pgaflags |= UVM_PGA_ZERO;
        prot = VM_PROT_READ | VM_PROT_WRITE;
 @@ -698,7 +700,7 @@ uvm_km_alloc_poolpage_cache(struct vm_ma
                return 0;
        KASSERT(!pmap_extract(pmap_kernel(), va, NULL));
  again:
 -      pg = uvm_pagealloc(NULL, 0, NULL, UVM_PGA_USERESERVE);
 +      pg = uvm_pagealloc(NULL, 0, NULL, waitok ? 0 : UVM_PGA_USERESERVE);
        if (__predict_false(pg == NULL)) {
                if (waitok) {
                        uvm_wait("plpg");
 @@ -724,7 +726,7 @@ uvm_km_alloc_poolpage(struct vm_map *map
        vaddr_t va;
  
   again:
 -      pg = uvm_pagealloc(NULL, 0, NULL, UVM_PGA_USERESERVE);
 +      pg = uvm_pagealloc(NULL, 0, NULL, waitok ? 0 : UVM_PGA_USERESERVE);
        if (__predict_false(pg == NULL)) {
                if (waitok) {
                        uvm_wait("plpg");
 Index: uvm_map.c
 ===================================================================
 RCS file: /cvsroot/src/sys/uvm/uvm_map.c,v
 retrieving revision 1.264
 diff -u -p -r1.264 uvm_map.c
 --- uvm_map.c  1 Dec 2008 10:54:57 -0000       1.264
 +++ uvm_map.c  3 Dec 2008 13:53:35 -0000
 @@ -4616,7 +4616,8 @@ again:
         * for simplicity, always allocate one page chunk of them at once.
         */
  
 -      pg = uvm_pagealloc(NULL, 0, NULL, 0);
 +      pg = uvm_pagealloc(NULL, 0, NULL,
 +          (flags & UVM_KMF_NOWAIT) != 0 ? UVM_PGA_USERESERVE : 0);
        if (__predict_false(pg == NULL)) {
                if (flags & UVM_FLAG_NOWAIT)
                        return NULL;
 Index: uvm_page.c
 ===================================================================
 RCS file: /cvsroot/src/sys/uvm/uvm_page.c,v
 retrieving revision 1.140
 diff -u -p -r1.140 uvm_page.c
 --- uvm_page.c 4 Jul 2008 10:56:59 -0000       1.140
 +++ uvm_page.c 3 Dec 2008 13:53:35 -0000
 @@ -1072,6 +1072,7 @@ uvm_pagealloc_strat(struct uvm_object *o
        struct uvm_cpu *ucpu;
        struct vm_page *pg;
        bool use_reserve;
 +      lwp_t *l;
  
        KASSERT(obj == NULL || anon == NULL);
        KASSERT(anon == NULL || off == 0);
 @@ -1079,6 +1080,15 @@ uvm_pagealloc_strat(struct uvm_object *o
        KASSERT(obj == NULL || mutex_owned(&obj->vmobjlock));
        KASSERT(anon == NULL || mutex_owned(&anon->an_lock));
  
 +      /*
 +       * make kernel reserve pages available if called by a kernel
 +       * thread or a realtime thread.
 +       */
 +      l = curlwp;
 +      if (__predict_true(l != NULL) && lwp_eprio(l) >= PRI_KTHREAD) {
 +              flags |= UVM_PGA_USERESERVE;
 +      }
 +
        mutex_spin_enter(&uvm_fpageqlock);
  
        /*
 Index: uvm_pdaemon.c
 ===================================================================
 RCS file: /cvsroot/src/sys/uvm/uvm_pdaemon.c,v
 retrieving revision 1.96
 diff -u -p -r1.96 uvm_pdaemon.c
 --- uvm_pdaemon.c      3 Dec 2008 11:43:51 -0000       1.96
 +++ uvm_pdaemon.c      3 Dec 2008 13:53:35 -0000
 @@ -294,20 +294,20 @@ uvm_pageout(void *arg)
  
                needsfree = uvmexp.free + uvmexp.paging < uvmexp.freetarg;
                needsscan = needsfree || uvmpdpol_needsscan_p();
 -              mutex_spin_exit(&uvm_fpageqlock);
  
                /*
                 * scan if needed
                 */
 -              if (needsscan)
 +              if (needsscan) {
 +                      mutex_spin_exit(&uvm_fpageqlock);
                        uvmpd_scan();
 +                      mutex_spin_enter(&uvm_fpageqlock);
 +              }
  
                /*
                 * if there's any free memory to be had,
                 * wake up any waiters.
                 */
 -
 -              mutex_spin_enter(&uvm_fpageqlock);
                if (uvmexp.free > uvmexp.reserve_kernel ||
                    uvmexp.paging == 0) {
                        wakeup(&uvmexp.free);
 @@ -870,7 +870,9 @@ uvmpd_scan_queue(void)
  
                if (swapcluster_allocslots(&swc)) {
                        mutex_exit(slock);
 +#if 0
                        dirtyreacts++; /* XXX */
 +#endif
                        continue;
                }