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    SubjectRe: [RFC PATCH 0/6] Do not call ->writepage[s] from direct reclaim and use a_ops->writepages() where possible
    On Tue, Jun 15, 2010 at 10:11:22AM -0400, Christoph Hellwig wrote:
    > On Tue, Jun 15, 2010 at 04:00:11PM +0200, Andrea Arcangeli wrote:
    > > collecting clean cache doesn't still satisfy the allocation), during
    > > allocations in direct reclaim and increase the THREAD_SIZE than doing
    > > this purely for stack reasons as the VM will lose reliability if we
    > This basically means doubling the stack size, as you can splice together
    > two extremtly stack hungry codepathes in the worst case. Do you really
    > want order 2 stack allocations?

    If we were forbidden to call ->writepage just because of stack
    overflow yes as I don't think it's big deal with memory compaction and
    I see this as a too limiting design to allow ->writepage only in
    kernel thread. ->writepage is also called by the pagecache layer,
    msync etc.. not just by kswapd.

    But let's defer this after we have any resemblance of hard numbers of
    worst-case stack usage measured during the aforementioned workload, I
    didn't read all the details as I'm quite against this design, but I
    didn't see any stack usage number or any sign of stack-overflow debug
    triggering. I'd suggest to measure the max stack usage first and worry

    And if ->writepage is a stack hog in some fs, I'd rather see
    ->writepage made less stack hungry (with proper warning at runtime
    with debug option enabled) than vetoed. The VM itself shouldn't be a
    stack hog already. I don't see a particular reason why writepage
    should be so stuck hungry compared to the rest of the kernel, it just
    have to do I/O, if it requires complex data structure it should
    kmalloc those and stay light on stack as everybody else.

    And if something I'm worried more about slab shrink than ->writepage
    as that enters the vfs layer and then the lowlevel fs to collect the
    dentry, inode etc...

     \ /
      Last update: 2010-06-15 16:25    [W:0.021 / U:11.548 seconds]
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