Re: [PATCH] mm: moving dirty pages balancing to pdfludh entirely

[Nikita Danilov <nikita@clusterfs.com>]

[Please, don't trim CC/To fields: LKML is too high traffic to read in
its entirety.]

Ananiev, Leonid I writes:
 >  Nikita Danilov writes:
 > > Wouldn't this interfere with current->backing_dev_info logic?
 > 
 > The proposed patch does not modify that logic.

Indeed, it *interferes* with it: in the original code, process doing
direct reclaim during balance_dirty_pages()

    generic_file_write()->balance_dirty_pages()->...->__alloc_pages()->...->pageout()

performs page-out even if queue is congested. Intent of this is to
throttle writers, and reduce risk of running oom (certain file systems,
especially ones with delayed allocation, tend to allocate a lot of
memory in balance_dirty_pages()->writepages() paths).

Your patch breaks this mechanism.

Nikita.
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