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    SubjectRe: [patch 0/7] cpuset writeback throttling
    On Wed, 5 Nov 2008 14:21:47 -0600 (CST)
    Christoph Lameter <> 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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      Last update: 2008-11-05 21:35    [W:0.030 / U:43.048 seconds]
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