Messages in this thread | | | Date | Thu, 24 Jun 2004 16:15:49 -0700 | From | William Lee Irwin III <> | Subject | Re: [discuss] Re: 32-bit dma allocations on 64-bit platforms |
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On Thu, Jun 24, 2004 at 04:09:45PM -0700, Andrew Morton wrote: > A testcase would be, on a 2G box: > a) free up as much memory as you can > b) write a 1.2G file to fill highmem with pagecache > c) malloc(800M), bzero(), sleep > d) swapoff -a > You now have a box which has almost all of lowmem pinned in anonymous > memory. It'll limp along and go oom fairly easily. > Another testcase would be: > a) free up as much memory as you can > b) write a 1.2G file to fill highmem with pagecache > c) malloc(800M), mlock it > You now have most of lowmem mlocked.
These are approximately identical to the testcases I had in mind, except neither of these is truly specific to 2GB and can have the various magic numbers calculated from sysconf() and/or meminfo.
On Thu, Jun 24, 2004 at 04:09:45PM -0700, Andrew Morton wrote: > In both situations the machine is really sick. Probably the most risky > scenario is a swapless machine in which lots of lowmem is allocated to > anonymous memory. > It should be the case that increasing lower_zone_peotection will fix all > the above. If not, it needs fixing. > So we're down the question "what should we default to at bootup". I find > it hard to justify defaulting to a mode where we're super-defensive against > this sort of thing, simply because nobody seems to be hitting the problems. > Distributors can, if the must, bump lower_zone_protection in initscripts, > and it's presumably pretty simple to write a boot script which parses > /proc/meminfo's MemTotal and SwapTotal lines, producing an appropriate > lower_zone_protection setting.
I'm going to beat on this in short order, but will be indisposed for an hour or two before that begins.
Thanks.
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