Re: kern/45718: processes sometimes get stuck and spin in vm_map

[Taylor R Campbell <campbell+netbsd%mumble.net@localhost>]

The following reply was made to PR kern/45718; it has been noted by GNATS.

From: Taylor R Campbell <campbell+netbsd%mumble.net@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/45718: processes sometimes get stuck and spin in vm_map
Date: Sun, 9 Dec 2012 08:12:19 +0000

    Date: Sun, 9 Dec 2012 07:25:25 +0000
    From: Taylor R Campbell <campbell+netbsd%mumble.net@localhost>
 
       Date: Sun, 9 Dec 2012 06:13:43 +0000
       From: Taylor R Campbell <campbell+netbsd%mumble.net@localhost>
 
       - I can still exec new processes, so the problem is *not* simply kva
       exhaustion causing the uvm_km_alloc in exec_pool_alloc to hang
       indefinitely waiting for kva -- all the requests for kva are for the
       same size, so if I can make new requests, the old ones should be
       serviceable too.
 
    This analysis was a little too simple-minded.  It may be that most new
    execs are serviced by exec_pool without going through exec_pool_alloc,
    but every one that does go through exec_pool_alloc gets wedged in [vm_ma=
 p].
 
 It also seems that although there is a hard limit on the number of
 objects currently pooled in exec_pool, namely maxexec (16 on my
 system), there is no limit on the number of pending calls to the
 pool's allocator.  This strikes me as suboptimal...