On Wed, Mar 20, 2024 at 09:35:39AM -0400, Stefan Hajnoczi wrote: > On Tue, Mar 19, 2024 at 08:10:49PM +0000, Daniel P. Berrangé wrote: > > On Tue, Mar 19, 2024 at 01:55:10PM -0400, Stefan Hajnoczi wrote: > > > On Tue, Mar 19, 2024 at 01:43:32PM +0000, Daniel P. Berrangé wrote: > > > > On Mon, Mar 18, 2024 at 02:34:29PM -0400, Stefan Hajnoczi wrote: > > > > > diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c > > > > > index 5fd2dbaf8b..2790959eaf 100644 > > > > > --- a/util/qemu-coroutine.c > > > > > +++ b/util/qemu-coroutine.c > > > > > > > > > +static unsigned int get_global_pool_hard_max_size(void) > > > > > +{ > > > > > +#ifdef __linux__ > > > > > + g_autofree char *contents = NULL; > > > > > + int max_map_count; > > > > > + > > > > > + /* > > > > > + * Linux processes can have up to max_map_count virtual memory > > > > > areas > > > > > + * (VMAs). mmap(2), mprotect(2), etc fail with ENOMEM beyond > > > > > this limit. We > > > > > + * must limit the coroutine pool to a safe size to avoid running > > > > > out of > > > > > + * VMAs. > > > > > + */ > > > > > + if (g_file_get_contents("/proc/sys/vm/max_map_count", &contents, > > > > > NULL, > > > > > + NULL) && > > > > > + qemu_strtoi(contents, NULL, 10, &max_map_count) == 0) { > > > > > + /* > > > > > + * This is a conservative upper bound that avoids exceeding > > > > > + * max_map_count. Leave half for non-coroutine users like > > > > > library > > > > > + * dependencies, vhost-user, etc. Each coroutine takes up 2 > > > > > VMAs so > > > > > + * halve the amount again. > > > > Leaving half for loaded libraries, etc is quite conservative > > if max_map_count is the small-ish 64k default. > > > > That reservation could perhaps a fixed number like 5,000 ? > > While I don't want QEMU to abort, once this heuristic is in the code it > will be scary to make it more optimistic and we may never change it. So > now is the best time to try 5,000. > > I'll send a follow-up patch that reserves 5,000 mappings. If that turns > out to be too optimistic we can increase the reservation.
BTW, I suggested 5,000, because I looked at a few QEM processes I have running on Fedora and saw just under 1,000 lines in /proc/$PID/maps, of which only a subset is library mappings. So multiplying that x5 felt like a fairly generous overhead for more complex build configurations. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|