Messages in this thread |  | | Date | Wed, 5 Nov 2008 12:31:50 -0800 | From | Andrew Morton <> | Subject | Re: [patch 0/7] cpuset writeback throttling |
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On Wed, 5 Nov 2008 14:21:47 -0600 (CST) Christoph Lameter <cl@linux-foundation.org> wrote:
> On Wed, 5 Nov 2008, Andrew Morton wrote: > > > > > Doable. lru->page->mapping->host is a good start. > > > > > > The block layer has a list of inodes that are dirty. From that we need to > > > select ones that will improve the situation from the cpuset/memcg. How > > > does the LRU come into this? > > > > In the simplest case, dirty-memory throttling can just walk the LRU > > writing back pages in the same way that kswapd does. > > That means running reclaim. But we are only interested in getting rid of > dirty pages. Plus the filesystem guys have repeatedly pointed out that > page sized I/O to random places in a file is not a good thing to do. There > was actually talk of stopping kswapd from writing out pages!
They don't have to be reclaimed.
> > There would probably be performance benefits in doing > > address_space-ordered writeback, so the dirty-memory throttling could > > pick a dirty page off the LRU, go find its inode and then feed that > > into __sync_single_inode(). > > We cannot call into the writeback functions for an inode from a reclaim > context. We can write back single pages but not a range of pages from an > inode due to various locking issues (see discussion on slab defrag > patchset).
We're not in a reclaim context. We're in sys_write() context.
> > But _are_ people hitting this problem? I haven't seen any real-looking > > reports in ages. Is there some workaround? If so, what is it? How > > serious is this problem now? > > Are there people who are actually having memcg based solutions deployed? > No enterprise release includes it yet so I guess that there is not much of > a use yet.
If you know the answer then please provide it. If you don't, please say "I don't know".
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