Date: Thu, 16 Jul 2020 02:43:37 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 248008] Post r358097 an i386 system can hang with many processes sleeping on btalloc Message-ID: <bug-248008-227-oKiYU0OFQF@https.bugs.freebsd.org/bugzilla/> In-Reply-To: <bug-248008-227@https.bugs.freebsd.org/bugzilla/> References: <bug-248008-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D248008 Rick Macklem <rmacklem@FreeBSD.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jeff@FreeBSD.org, | |kib@FreeBSD.org, | |rlibby@freebsd.org --- Comment #2 from Rick Macklem <rmacklem@FreeBSD.org> --- Sorry, the comments got messed up. I guess I shouldn't have done the attachment before submitting or something.. Anyhow, here is what has gone on. Post r358097 (it took a while to bisect to this commit), running a kernel build over NFS on an i386 system (I also got it once doing the build on UFS), I've gotten hangs with many processes sleeping on "btalloc". Ryan Libby made the following suggestions and I implemented #2, which fixed the hangs. I think the patch is not complete. It looks like the problem is that for systems that do not have UMA_MD_SMALL_ALLOC, we do uma_zone_set_allocf(vmem_bt_zone, vmem_bt_alloc); but we haven't set an appropriate free function. This is probably why UMA_ZONE_NOFREE was originally there. When NOFREE was removed, it was appropriate for systems with uma_small_alloc. So by default we get page_free as our free function. That calls kmem_free, which calls vmem_free ... but we do our allocs with vmem_xalloc. I'm not positive, but I think the problem is that in effect we vmem_xalloc -> vmem_free, not vmem_xfree. Three possible fixes: 1: The one you tested, but this is not best for systems with uma_small_alloc. 2: Pass UMA_ZONE_NOFREE conditional on UMA_MD_SMALL_ALLOC. 3: Actually provide an appropriate vmem_bt_free function. I think we should just do option 2 with a comment, it's simple and it's what we used to do. I'm not sure how much benefit we would see from option 3, but it's more work. --=20 You are receiving this mail because: You are the assignee for the bug.=
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