Messages in this thread | | | Date | Tue, 16 Jan 2007 23:00:34 -0800 | From | Andrew Morton <> | Subject | Re: [RFC 0/8] Cpuset aware writeback |
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> On Tue, 16 Jan 2007 22:27:36 -0800 (PST) Christoph Lameter <clameter@sgi.com> wrote: > On Tue, 16 Jan 2007, Andrew Morton wrote: > > > > Yes this is the result of the hierachical nature of cpusets which already > > > causes issues with the scheduler. It is rather typical that cpusets are > > > used to partition the memory and cpus. Overlappig cpusets seem to have > > > mainly an administrative function. Paul? > > > > The typical usage scenarios don't matter a lot: the examples I gave show > > that the core problem remains unsolved. People can still hit the bug. > > I agree the overlap issue is a problem and I hope it can be addressed > somehow for the rare cases in which such nesting takes place. > > One easy solution may be to check the dirty ratio before engaging in > reclaim. If the dirty ratio is sufficiently high then trigger writeout via > pdflush (we already wakeup pdflush while scanning and you already noted > that pdflush writeout is not occurring within the context of the current > cpuset) and pass over any dirty pages during LRU scans until some pages > have been cleaned up. > > This means we allow allocation of additional kernel memory outside of the > cpuset while triggering writeout of inodes that have pages on the nodes > of the cpuset. The memory directly used by the application is still > limited. Just the temporary information needed for writeback is allocated > outside.
Gad. None of that should be necessary.
> Well sounds somehow still like a hack. Any other ideas out there?
Do what blockdevs do: limit the number of in-flight requests (Peter's recent patch seems to be doing that for us) (perhaps only when PF_MEMALLOC is in effect, to keep Trond happy) and implement a mempool for the NFS request critical store. Additionally:
- we might need to twiddle the NFS gfp_flags so it doesn't call the oom-killer on failure: just return NULL.
- consider going off-cpuset for critical allocations. It's better than going oom. A suitable implementation might be to ignore the caller's cpuset if PF_MEMALLOC. Maybe put a WARN_ON_ONCE in there: we prefer that it not happen and we want to know when it does.
btw, regarding the per-address_space node mask: I think we should free it when the inode is clean (!mapping_tagged(PAGECACHE_TAG_DIRTY)). Chances are, the inode will be dirty for 30 seconds and in-core for hours. We might as well steal its nodemask storage and give it to the next file which gets written to. A suitable place to do all this is in __mark_inode_dirty(I_DIRTY_PAGES), using inode_lock to protect address_space.dirty_page_nodemask. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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