Re: [PATCH 61 of 66] use compaction for GFP_ATOMIC order > 0

[KOSAKI Motohiro]

> From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> 
> This takes advantage of memory compaction to properly generate pages of order >
> 0 if regular page reclaim fails and priority level becomes more severe and we
> don't reach the proper watermarks.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>

First, I don't think this patch is related to GFP_ATOMIC. So, I think the 
patch title is a bit misleading.

Second, this patch has two changes. 1) remove PAGE_ALLOC_COSTLY_ORDER 
threshold 2) implement background compaction. please separate them.

Third, This patch makes a lot of PFN order page scan and churn LRU
aggressively. I'm not sure this aggressive lru shuffling is safe and
works effective. I hope you provide some demonstration and/or show 
benchmark result.

Thanks.



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