Re: [PATCH] mm: get rid of __alloc_pages_high_priority

From: Mel Gorman
Date: Fri Nov 13 2015 - 05:18:44 EST

On Thu, Nov 12, 2015 at 04:53:38PM +0100, mhocko@xxxxxxxxxx wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> __alloc_pages_high_priority doesn't do anything special other than it
> calls get_page_from_freelist and loops around GFP_NOFAIL allocation
> until it succeeds. It would be better if the first part was done in
> __alloc_pages_slowpath where we modify the zonelist because this would
> be easier to read and understand. And do the retry at the very same
> place because retrying without even attempting to do any reclaim is
> fragile because we are basically relying on somebody else to make the
> reclaim (be it the direct reclaim or OOM killer) for us. The caller
> might be holding resources (e.g. locks) which block other other
> reclaimers from making any progress for example.
> Remove the helper and open code it into its only user. We have to be
> careful about __GFP_NOFAIL allocations from the PF_MEMALLOC context
> even though this is a very bad idea to begin with because no progress
> can be gurateed at all. We shouldn't break the __GFP_NOFAIL semantic
> here though. It could be argued that this is essentially GFP_NOWAIT
> context which we do not support but PF_MEMALLOC is much harder to check
> for existing users because they might happen deep down the code path
> performed much later after setting the flag so we cannot really rule out
> there is no kernel path triggering this combination.
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

Mel Gorman
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