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    SubjectRe: [RFC 0/3] Recursive reclaim (on __PF_MEMALLOC)
    On Thu, 13 Sep 2007, Peter Zijlstra wrote:

    > > > Every user of memory relies on the VM, and we only get into trouble if
    > > > the VM in turn relies on one of these users. Traditionally that has only
    > > > been the block layer, and we special cased that using mempools and
    > > > PF_MEMALLOC.
    > > >
    > > > Why do you object to me doing a similar thing for networking?
    > >
    > > I have not seen you using mempools for the networking layer. I would not
    > > object to such a solution. It already exists for other subsystems.
    > Dude, listen, how often do I have to say this: I cannot use mempools for
    > the network subsystem because its build on kmalloc! What I've done is
    > build a replacement for mempools - a reserve system - that does work
    > similar to mempools but also provides the flexibility of kmalloc.
    > That is all, no more, no less.

    Its different since it becomes a privileged player that can suck all
    the available memory out of the page allocator.

    > I'm confused by this, I've never claimed part of, or such a thing. All
    > I'm saying is that because of the circular dependency between the VM and
    > the IO subsystem used for swap (not file backed paging [*], just swap)
    > you have to do something special to avoid deadlocks.

    How are dirty file backed pages different? They may also be written out
    by the VM during reclaim.

    > > Replacing the mempools for the block layer sounds pretty good. But how do
    > > these various subsystems that may live in different portions of the system
    > > for various devices avoid global serialization and livelock through your
    > > system?
    > The reserves are spread over all kernel mapped zones, the slab allocator
    > is still per cpu, the page allocator tries to get pages from the nearest
    > node.

    But it seems that you have unbounded allocations with PF_MEMALLOC now for
    the networking case? So networking can exhaust all reserves?

    > > And how is fairness addresses? I may want to run a fileserver on
    > > some nodes and a HPC application that relies on a fiberchannel connection
    > > on other nodes. How do we guarantee that the HPC application is not
    > > impacted if the network services of the fileserver flood the system with
    > > messages and exhaust memory?
    > The network system reserves A pages, the block layer reserves B pages,
    > once they start getting pages from the reserves they go bean counting,
    > once they reach their respective limit they stop.

    That sounds good.
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      Last update: 2007-09-13 20:35    [W:0.026 / U:2.380 seconds]
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