Re: 2.5.48-mm1

[Hugh Dickins <hugh@veritas.com>]

On Tue, 19 Nov 2002, Andrew Morton wrote:
> 
> +loop-balance-pages.patch
> 
>  Small optimisation to loop

I disagree with this one (changing balance_dirty_pages to _ratelimited
when loop_thread writes to file): it's a step in the right direction,
but I think you should remove that balance_dirty_pages call completely.

I'm experimenting with what's needed to prevent deadoralivelock in
loop over tmpfs under heavy memory pressure (thank you for eliminating
wait_on_page_bit from shrink_list!).  One element of that is to ignore
balance_dirty_pages below loop (I hadn't noticed the explicit call,
offhand I'm unsure whether that's the only possible instance).

The loop_thread is working towards undirtying memory (completing
writeback): a loop of blk_congestion_waits is appropriate at the
upper level where the user task generating dirt needs to be throttled,
but I don't believe it's appropriate at this level - we wouldn't want
to throttle the disk, no more should we throttle the loop_thread.

Hugh

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