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    SubjectRe: [PATCH] mm: moving dirty pages balancing to pdfludh entirely
    Date
    Ananiev, Leonid I writes:
    > Nikita Danilov wtites:
    > > performs page-out even if queue is congested.
    > Yes. If user thread which generates dirty pages need in
    > reclaimed memory it consider own dirty page as candidate for page-out.
    > It functions as before patching.
    >
    > > Intent of this is to throttle writers.
    > I suppose you means dirtier or write(2) caller but not writepage()
    > caller. The dirtier is throttled with backing_dev_info logic as before
    > patching.

    I meant ->writepages() used by balance_dirty_pages(), see below.

    >
    > While pdflush thread sorts pages for page-out it does not
    > consider as a candidate a page to be written with congested queue.
    > Pdflush thread functions as before patching. Pdflush tends to make pages
    > un-dirty without overload memory or IO and it is not need to let pdflush

    This assumption is valid for ext2, where ->writepages() simply sends
    pages to the storage, but other file systems (like reiser4) do a *lot*
    of work in ->writepages() path, allocating quite an amount of memory
    before starting write-out. With your patch, this work is done from
    pdflush, and won't be throttled by may_write_to_queue() check, thus
    increasing a risk of allocation failure.

    > do page-out with congested queue as you have proposed.
    >
    > Leonid

    Nikita.
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