On Sat, Nov 07, 2015 at 04:04:00AM +0000, Adrian Chadd wrote: A> Author: adrian A> Date: Sat Nov 7 04:04:00 2015 A> New Revision: 290481 A> URL: https://svnweb.freebsd.org/changeset/base/290481 A> A> Log: A> Add a sched_yield() to work around low memory conditions in the current code. A> A> Things seem to get stuck in low memory conditions where no bufs are available, A> the reclamation path is called to wakeup the daemon, but no sleeping is done. A> Because of this, we are stuck in a tight loop in the current process and A> never run said reclamation path. A> A> This was introduced in r289279 . This is only a temporary workaround A> to restore system usefulness until the more permanent solutions can be A> found. A> A> Tested: A> A> * Carambola2, 64MB (and 32MB by manual config.) A> A> Modified: A> head/sys/kern/vfs_bio.c A> A> Modified: head/sys/kern/vfs_bio.c A> ============================================================================== A> --- head/sys/kern/vfs_bio.c Sat Nov 7 02:18:19 2015 (r290480) A> +++ head/sys/kern/vfs_bio.c Sat Nov 7 04:04:00 2015 (r290481) A> @@ -3622,6 +3622,23 @@ loop: A> if (bp == NULL) { A> if (slpflag || slptimeo) A> return NULL; A> + /* A> + * XXX This is here until the sleep path is diagnosed A> + * enough to work under very low memory conditions. A> + * A> + * There's an issue on low memory, 4BSD+non-preempt A> + * systems (eg MIPS routers with 32MB RAM) where buffer A> + * exhaustion occurs without sleeping for buffer A> + * reclaimation. This just sticks in a loop and A> + * constantly attempts to allocate a buffer, which A> + * hits exhaustion and tries to wakeup bufdaemon. A> + * This never happens because we never yield. A> + * A> + * The real solution is to identify and fix these cases A> + * so we aren't effectively busy-waiting in a loop A> + * until the reclaimation path has cycles to run. A> + */ A> + kern_yield(PRI_USER); A> goto loop; A> }
It'll be nice if such crutches have a test case in src/tests, and a reference to it in the comment above. So that in future, someone considering that the crutch is no longer needed, can quickly check that assumption. -- Totus tuus, Glebius. _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "[email protected]"
