Re: [RFC] Remove temp_priority

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Martin J. Bligh wrote:
Coming from another angle, I am thinking about doing away with direct
reclaim completely. That means we don't need any GFP_IO or GFP_FS, and
solves the problem of large numbers of processes stuck in reclaim and
skewing aging and depleting the memory reserve.


Last time I proposed that, the objection was how to throttle the heavy
dirtiers so they don't fill up RAM with dirty pages?

Now that we have the dirty mmap accounting, page dirtiers should be
throttled pretty well via page writeback throttling.

Also, how do you do atomic allocations? Create a huge memory pool and
pray really hard?

Well, yes. Atomic allocations as of *today* cannot do any reclaim, and
thus they rely on kswapd to free their memory, and we keep a (not huge)
memory pool for them. They also have to be able to handle failures, and
by and large they do OK.

But that's tricky because we don't have enough kswapds to get maximum
reclaim throughput on many configurations (only single core opterons
and UP systems, really).


It's not a question of enough kswapds. It's that we can dirty pages
faster than they can possibly be written to disk.

dd if=/dev/zero of=/tmp/foo

You can't catch that at the allocation side anyway because clean pagecache
may already exist for /tmp/foo.

We've always done pretty well (in 2.6) with correctly throttling and
limiting write(2) writes into pagecache, haven't we?

--
SUSE Labs, Novell Inc.
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