linux-kernel - Re: [PATCH 1/2] mm: thp: relax __GFP_THISNODE for MADV

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Message-ID: <19684def-0ab4-6ca6-767d-2364cc459740@suse.cz>
Date:   Tue, 9 Oct 2018 15:08:03 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Cc:     Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Argangeli <andrea@...nel.org>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>,
        "Kirill A. Shutemov" <kirill@...temov.name>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Stable tree <stable@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 1/2] mm: thp: relax __GFP_THISNODE for MADV_HUGEPAGE
 mappings

On 10/8/18 10:41 PM, David Rientjes wrote:
> +			/*
> +			 * If faulting a hugepage, it is very unlikely that
> +			 * thrashing the zonelist is going to assist compaction
> +			 * in freeing an entire pageblock.  There are no
> +			 * guarantees memory compaction can free an entire
> +			 * pageblock under such memory pressure that it is
> +			 * better to simply fail and fallback to native pages.
> +			 */
> +			if (order == pageblock_order &&
> +					!(current->flags & PF_KTHREAD))
> +				goto nopage;

After we got rid of similar hardcoded heuristics, I would be very
unhappy to start adding them back. A new gfp flag is also unfortunate,
but more acceptable to me.

> +
>  			/*
>  			 * Looks like reclaim/compaction is worth trying, but
>  			 * sync compaction could be very expensive, so keep
>