> > The other deadlock, in throttle_vm_writeout() is still to be solved.
>
> Let's go back to the original changelog:
>
> Author: marcelo.tosatti <marcelo.tosatti>
> Date: Tue Mar 8 17:25:19 2005 +0000
>
> [PATCH] vm: pageout throttling
>
> With silly pageout testcases it is possible to place huge amounts of memory
> under I/O. With a large request queue (CFQ uses 8192 requests) it is
> possible to place _all_ memory under I/O at the same time.
>
> This means that all memory is pinned and unreclaimable and the VM gets
> upset and goes oom.
>
> The patch limits the amount of memory which is under pageout writeout to be
> a little more than the amount of memory at which balance_dirty_pages()
> callers will synchronously throttle.
>
> This means that heavy pageout activity can starve heavy writeback activity
> completely, but heavy writeback activity will not cause starvation of
> pageout. Because we don't want a simple `dd' to be causing excessive
> latencies in page reclaim.
>
> Signed-off-by: Andrew Morton <[email protected]>
> Signed-off-by: Linus Torvalds <[email protected]>
>
> (A good one! I wrote it ;))
>
>
> I believe that the combination of dirty-page-tracking and its calls to
> balance_dirty_pages() mean that we can now never get more than dirty_ratio
> of memory into the dirty-or-writeback condition.
>
> The vm scanner can convert dirty pages into clean, under-writeback pages,
> but it cannot increase the total of dirty+writeback.
What about swapout? That can increase the number of writeback pages,
without decreasing the number of dirty pages, no?
Miklos
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