On 08/23/2012 11:31, Luigi Rizzo wrote:
On Thu, Aug 23, 2012 at 10:48:27AM -0500, Alan Cox wrote:
On Wed, Aug 22, 2012 at 7:01 AM, Luigi Rizzo<ri...@iet.unipi.it> wrote:
I am trying to make netmap adapt the amount of memory it allocates
to what is available. At its core, it uses contigmalloc() with
small chunks (even down to 1 page) to fetch memory.
Problem is, i notice that before failing, contigmalloc()
tries to swap out some processes (effectively killing them
because i have no swap configured in my picobsd image).
This happens with both M_WAITOK and M_NOWAIT, the difference
is only in the number of retries it does -- see e.g.
sys/vm/vm_kern.c :: kmem_alloc_contig()
where it retries once for M_NOWAIT and 3 times for M_WAITOK.
I wonder if there is a way to make contigmalloc less aggressive
and fail without killing those innocent processes ?
Have you actually observed processes being killed with M_NOWAIT?
The difference between M_NOWAIT and M_WAITOK is more than just the number
of retries. Each successive iteration is more aggressive in its attempt to
recover pages. On the first iteration, no pages should be written to
swap. Nothing should happen that could result in process termination.
yes i do see that.
Maybe less aggressive with M_NOWAIT but still kills processes.
Are you compiling world with MALLOC_PRODUCTION? The latest version of
jemalloc uses significantly more memory when debugging options are
enabled. This first came up in a thread titled "10-CURRENT and swap
usage" back in June.
Even at its most aggressive, M_WAITOK, contigmalloc() does not directly
kill processes. If process death coincides with the use of
contigmalloc(), then it is simply the result of earlier, successful
contigmalloc() calls, or for that matter any other physical memory
allocation calls, having depleted the pool of free pages to the point
that the page daemon runs and invokes vm_pageout_oom().
Here is what i get with a kernel on a qemu machine with not enough
memory. This output comes when the kernel is looping around
a contigmalloc, getting one page at a time (i have rate-limited
prints). The function is netmap_finalize_obj_allocator(),
it works for a while, then decides to kill some processes,
keeps succeeding, kills some other processes, etc.
Eventually memory is over and you see the 'Unable to create...'
message at the end.
...
269.005884 netmap_finalize_obj_allocator [593] cluster at 63182 ok
PicoBSD (default) (ttyv0)
login: pid 60 (getty), uid 0, was killed: out of swap space
pid 63 (init), uid 0, was killed: out of swap space
pid 62 (init), uid 0, was killed: out of swap space
pid 61 (init), uid 0, was killed: out of swap space
pid 64 (init), uid 0, was killed: out of swap space
pid 51 (getty), uid 0, was killed: out of swap space
pid 50 (getty), uid 0, was killed: out of swap space
pid 65 (init), uid 0, was killed: out of swap space
pid 49 (getty), uid 0, was killed: out of swap space
pid 48 (getty), uid 0, was killed: out of swap space
pid 47 (getty), uid 0, was killed: out of swap space
pid 57 (pkt-gen), uid 0, was killed: out of swap space
269.602751 netmap_finalize_obj_allocator [600] Unable to create cluster at
95452 for 'netmap_buf' allocator
If that helps, on this machine i have no swap configured
(it is a picobsd image run within qemu)
cheers
luigi
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