Date: Mon, 28 Jan 2013 00:09:17 -0600 From: Alan Cox <alan.l.cox@gmail.com> To: Ian Lepore <ian@freebsd.org> Cc: freebsd-current@freebsd.org, Andre Oppermann <andre@freebsd.org> Subject: Re: Trouble with recent auto-tuning changes Message-ID: <CAJUyCcOGE-86Y_fMkFyDwORd%2Bve0mpwrePv5uSey0L-mfD-9bA@mail.gmail.com> In-Reply-To: <1359310302.93359.48.camel@revolution.hippie.lan> References: <1359310302.93359.48.camel@revolution.hippie.lan>
next in thread | previous in thread | raw e-mail | index | archive | help
On Sun, Jan 27, 2013 at 12:11 PM, Ian Lepore <ian@freebsd.org> wrote: > I ran into a panic while attempting to un-tar a large file on a > DreamPlug (arm-based system) running -current. The source and dest of > the un-tar is the root filesystem on sdcard, and I get this: > > panic: kmem_malloc(4096): kmem_map too small: 12582912 total allocated > > Just before the panic I see the tar process get hung in a "nokva" wait. > 12582912 is the value of VM_KMEM_SIZE from arm/include/vmparam.h. > > In r245575 the init order for mbuf limits was changed from > SI_SUB_TUNABLES to SI_SUB_KMEM so that mbuf limits could be based on the > results of sizing kernel memory. Unfortunately, the process of sizing > kernel memory relies on the mbuf limits; in kmeminit(): > > vm_kmem_size = VM_KMEM_SIZE + nmbclusters * PAGE_SIZE; > > Since r245575, nmbclusters is zero when this line of code runs. If I > manually plugin "32768" (the number tunable_mbinit() comes up with for > this platform) in that line, the panic stops happening. > > So we've got two problems here... one is the circular dependency in > calculating the mbuf limits. The other is the fact that some > non-trivial amount of kernel memory we're allowing for mbufs is actually > being used for other things. That is, if my system was actually using > all the mbufs that tunable_mbinit() allowed for, then this panic while > untarring a huge file would still have happened. > > All of this is factually correct. However, it's a red herring. The real problem is that arm, unlike every other architecture in the tree, does not enable auto-sizing of the kmem map based on the physical memory size. Specifically, you'll find VM_KMEM_SIZE_SCALE defined in "arch"/include/vmparam.h on every other architecture, just not on arm. This auto-sizing overrides the value of VM_KMEM_SIZE. > I arrive at the latter conclusion based on the fact that this panic > happens even if no network interfaces (other than lo0) are configured. > That is, nmbclusters == 0 is a reasonable approximation of my need for > network mbufs. So something in the system needs to be taken into > account when sizing kernel memory to allow for whatever it is about > untarring a huge file that eats kernel memory (buffer cache?). > > I can easily reproduce this if you need me to gather any specific info. > > -- Ian > > > _______________________________________________ > freebsd-current@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org" >
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAJUyCcOGE-86Y_fMkFyDwORd%2Bve0mpwrePv5uSey0L-mfD-9bA>