Re: [PATCH] vmscan: do not throttle kthreads due to too_many_isolated

[Vladimir Davydov <vdavydov@virtuozzo.com>]

On Wed, Nov 25, 2015 at 04:45:13PM +0100, Vlastimil Babka wrote:
> On 11/25/2015 04:36 PM, Vladimir Davydov wrote:
> > Block device drivers often hand off io request processing to kernel
> > threads (example: device mapper). If such a thread calls kmalloc, it can
> > dive into direct reclaim path and end up waiting for too_many_isolated
> > to return false, blocking writeback. This can lead to a dead lock if the
> 
> Shouldn't such allocation lack __GFP_IO to prevent this and other kinds of
> deadlocks? And/or have mempools?

Not necessarily. loopback is an example: it can call
grab_cache_write_begin -> add_to_page_cache_lru with GFP_KERNEL.

> PF_KTHREAD looks like a big hammer to me that will solve only one
> potential problem...

This problem can result in processes hanging forever. Any ideas how this
could be fixed in a better way?

Thanks,
Vladimir

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