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    SubjectRe: [PATCH 2/2] percpu_counter: Put a reasonable upper bound on percpu_counter_batch

    Hi Ted,

    > I understand why we would want to reduce this number.
    > Unfortunately, the question is what do we do if all 1024 threads try
    > to do buffered writes into the file system at the same instant, when
    > we have less than 4 megabytes of space left?
    > The problem is that we can then do more writes than we have space, and
    > we will only find out about it at write back time, when the process
    > may have exited already -- at which point data loss is almost
    > inevitable. (We could keep the data in cache and frantically page
    > the system administrator to delete some files to make room for dirty
    > data, but that's probably not going to end well….)
    > What we can do if we must clamp this threshold is to also increase the
    > threshold at which we shift away from delayed allocation. We'll then
    > allocate each block at write time, which does mean more CPU and
    > less efficient allocation of blocks, but if we're down to our last 4
    > megabytes, there's probably not much we can do that will be efficient
    > as far as block layout anyway….

    Thanks for the explanation, I'll go back and take another look.

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