Date: Mon, 28 Nov 2016 19:22:40 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Fabian Keil <freebsd-listen@fabiankeil.de>, freebsd-hackers@freebsd.org, David Cross <dcrosstech@gmail.com> Subject: Re: FreeBSD 11 i386 disk deadlock (I think) (now with reproduction steps!) Message-ID: <20161128162240.GM99742@zxy.spb.ru> In-Reply-To: <20161128160311.GQ54029@kib.kiev.ua> References: <CAM9edeMYMhnkWid7Lig5D-FjhahniFm0VbFRm8ysyb85h29wXg@mail.gmail.com> <20161128041847.GA65249@charmander> <20161128120046.GP54029@kib.kiev.ua> <CAM9edeNDWcJ7R_%2B_Q%2BMksVcL_pcJVR%2BO7t98s5XyfmOpXgc-zw@mail.gmail.com> <20161128144135.10f93205@fabiankeil.de> <20161128160311.GQ54029@kib.kiev.ua>
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On Mon, Nov 28, 2016 at 06:03:11PM +0200, Konstantin Belousov wrote: > On Mon, Nov 28, 2016 at 02:43:30PM +0100, Fabian Keil wrote: > > David Cross <dcrosstech@gmail.com> wrote: > > > > > This is certainly new behavior, or a new manifestation. > > > > Recently a couple of uma consumers were changed to share uma zones > > instead of using a dedicated zone. As a result geli competes with > > more uma consumers and is more likely to deadlock. The bug isn't > > new, it's just triggered more often now. > The problem happens on layer much lower than UMA, it is whole reusable > page pool which is depleted and cannot be re-filled without allocating > more memory. If you think about it, the deadlock is obviously trivial: > pagedaemon is the main source of the free pages, but if producing free > page requires allocating one, low memory condition is equal to deadlock. > > It was always there, in the sense that for all versions of freebsd, if > file/disk write path requires memory allocation, there is the trouble. > > For geom, some special unique measures were taken so that bio allocations > do not cause the issue in typical situations. Typical workaround for this is pre-allocate some memory for this operation.
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