A panic by vm_pageout_scan_active activity, some details in case they might help

I tried a poudriere(-devel) bulk -Ca on the amd64 system that
I have access to and a package build used up much of the
RAM+SWAP == 704 GiBytes before a panic happened. Past examples
OOM'd without panics, although I did not know the context until
examining this crash dump.

# uname -apKU
FreeBSD 7950X3D-ZFS 15.0-CURRENT FreeBSD 15.0-CURRENT main-n278320-3a33e39edd48 GENERIC-NODEBUG amd64 amd64 1500048 1500048

That is an official PkgBase installation of the boot-kernel and
boot-world, not a personal build.

The dump materials had references for doxygen and for dot to :

/usr/local/poudriere/data/.m/main-ZNV4-bulk_a-alt/06/dev

that let me track this to the [06] builder running at the time
of the crash:

[2D:01:22:29] [06] [00:00:00] Building   graphics/sdl2_gpu | sdl2_gpu-0.12.0

It was running doxygen, which in turn was running mulitple dot's.

From /var/crash/core.txt.4 :

UID   PID  PPID  C PRI NI       VSZ      RSS MWCHAN   STAT TT          TIME COMMAND
. . .
  0 79229 40923  4  59  0     23524     4148 wait     D     -       0:00.00 [sh]
  0 79230 79229  5  59  0     14208      172 wait     Ds    -       0:00.01 [make]
  0 79233 79230  4  59  0     14668      176 wait     D     -       0:00.00 [sh]
  0 79234 79233  5  59  0     14668      176 wait     D     -       0:00.00 [sh]
  0 79235 79234 12   0  0     16284      356 select   D     -       0:00.01 [ninja]
  0 79236 79235 28  59  0    223048     1052 uwait    D     -       0:00.44 [doxygen]
  0 79272 79236 25  59  0 157589964 41424308 pfault   D     -       3:25.33 [dot]
  0 79279 79236 31  59  0 157601740 41513520 pfault   D     -       3:23.41 [dot]
  0 79289 79236 14  59  0 157589964 41361600 pfault   D     -       3:22.72 [dot]
  0 79301 79236 18  49  0 157667276 41208476 pfault   D     -       3:24.32 [dot]
. . .

. . .
#14 <signal handler called>
No locals.
#15 vm_pageout_scan_active (vmd=0xffffffff81c22380 <vm_dom>,
    page_shortage=102849)
    at /home/pkgbuild/worktrees/main/sys/vm/vm_pageout.c:1264
        ss = {bq = {bq_pa = {0xfffffe0030a1e500, 0xfffffe00a8798110,
              0xfffffe00e3083e30, 0xfffffe00a47a4228, 0xfffffe002b6d8ef8,
              0xfffffe0065cf29a0, 0xfffffe007a1b83b8, 0xfffffe008cf7b3c0,
              0xfffffe005cd565e0, 0xfffffe0048ced5d8, 0xfffffe00c761d488,
              0xfffffe008a5efe90, 0xfffffe00cf341738, 0xfffffe00413f97b8,
              0xfffffe005270cc68, 0xfffffe00a5d9d690, 0xfffffe00294329e0,
              0xfffffe005ef52f00, 0xfffffe0020dff308, 0xfffffe00ce1e9a40,
              0xfffffe007ec47618, 0xfffffe005d1ba7e8, 0xfffffe0032d73470,
              0xfffffe0030835e88, 0xfffffe009969c438, 0xfffffe00f151b0c8,
              0xfffffe0063916fe8, 0xfffffe00dac0b778, 0xfffffe0016267348,
              0xfffffe00b74a5fe0, 0xfffffe003434ef80, 0xfffffe009e31e840,
              0xfffffe00530f6408, 0xfffffe00e0649508, 0xfffffe0102e87ad8,
              0xfffffe0092c52848, 0xfffffe00ba829618, 0xfffffe008bf0fd10,
              0xfffffe00550708c0, 0xfffffe00eedc67b8, 0xfffffe00d45f8210,
              0xfffffe00b89a8698, 0xfffffe0082ffb310, 0xfffffe00accd53c0,
              0xfffffe0091c8f5d8, 0xfffffe004e20f180, 0xfffffe004dfb4f90,
              0xfffffe00a437fbb0, 0xfffffe00218cb698, 0xfffffe004ee5d278,
              0xfffffe00a9e845a0, 0xfffffe0025d4a7c8, 0xfffffe0037612ac8,
              0xfffffe005c7d3da8, 0xfffffe00d307c1b8, 0xfffffe00ee416538,
              0xfffffe0043747508, 0xfffffe00ef30b508, 0xfffffe00c04de600,
              0xfffffe008c0e3040, 0xfffffe0071a97b40, 0xfffffe005b644ad8,
              0xfffffe00dd5da3b0}, bq_cnt = 39},
          pq = 0xffffffff81c22400 <vm_dom+128>,
          marker = 0xffffffff81c22778 <vm_dom+1016>, maxscan = 37165731,
          scanned = 15440544}
        marker = 0xffffffff81c22778 <vm_dom+1016>
        pq = 0xffffffff81c22400 <vm_dom+128>
        old = <optimized out>
        scan_tick = <optimized out>
        min_scan = <optimized out>
        m = 0xfffffe00eedc67b8
        object = 0x2b6c70f000
        refs = <optimized out>
        new = <optimized out>
        ps_delta = <optimized out>
        act_delta = <optimized out>
        max_scan = <optimized out>
        nqueue = <optimized out>
        _v = <optimized out>
        _tid = <optimized out>
        _v = <optimized out>
        _tid = <optimized out>
        _v = <optimized out>
        _v = <optimized out>
        _tid = <optimized out>
        _v = <optimized out>
. . .

From the /usr/src/sys/ for the PkgBase installation in use, there is in
vm_pageout_scan_active :

/home/pkgbuild/worktrees/main/sys/vm/vm_pageout.c: unmodified, readonly: line 1264 of 2416 [52%]

                /*
                 * Check to see "how much" the page has been used.
                 *
                 * Test PGA_REFERENCED after calling pmap_ts_referenced() so
                 * that a reference from a concurrently destroyed mapping is
                 * observed here and now.
                 *
                 * Perform an unsynchronized object ref count check.  While
                 * the page lock ensures that the page is not reallocated to
                 * another object, in particular, one with unmanaged mappings
                 * that cannot support pmap_ts_referenced(), two races are,
                 * nonetheless, possible:
                 * 1) The count was transitioning to zero, but we saw a non-
                 *    zero value.  pmap_ts_referenced() will return zero
                 *    because the page is not mapped.
                 * 2) The count was transitioning to one, but we saw zero.
                 *    This race delays the detection of a new reference.  At
                 *    worst, we will deactivate and reactivate the page.
                 */
                refs = object->ref_count != 0 ? pmap_ts_referenced(m) : 0;

I am unlikely to be able to replicate the panic.

I hope that this is of some use.

Note:

I linked /home/pkgbuild/worktrees/main/sys to
/usr/sys/src so that such paths work in my
context.

===
Mark Millard
marklmi at yahoo.com