I was testing the new fuse shared writable mmap support, and finding
that bash-shared-mapping deadlocks (which isn't so strange ;). What
is more strange is that this is not an OOM situation at all, with
plenty of free and cached pages.
A little more investigation shows that a similar deadlock happens
reliably with bash-shared-mapping on a loopback mount, even if only
half the total memory is used.
The cause is slightly different in the two cases:
- loopback mount: allocation by the underlying filesystem is stalled
on throttle_vm_writeout()
- fuse-loop: page dirtying on the underlying filesystem is stalled on
balance_dirty_pages()
In both cases the underlying fs is totally innocent, with no
dirty/writback pages, yet it's waiting for the global dirty+writeback
to go below the threshold, which obviously won't, until the
allocation/dirtying succeeds.
I'm not quite sure what the solution is, and asking for thoughts.
Ideas:
- per filesystem dirty counters. If filesystem is clean (or dirty
is below some minimum), then balance_dirty_pages() should no wait
any more
- throttle_vm_writeout() was meant to throttle swapping, no? So in
that case there should be a separate swap-writback counter
Thanks,
Miklos
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
