linux-kernel - Re: [PATCH v2 1/4] mm/page_alloc: fix non cma alloc context

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Message-Id: <20200720161613.15cddfdc2247377347f5471f@linux-foundation.org>
Date:   Mon, 20 Jul 2020 16:16:13 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     js1304@...il.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@....com, Vlastimil Babka <vbabka@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/4] mm/page_alloc: fix non cma alloc context

On Mon, 20 Jul 2020 13:56:15 +0900 js1304@...il.com wrote:

> Currently, preventing cma area in page allocation is implemented by using
> current_gfp_context(). However, there are two problems of this
> implementation.
> 
> First, this doesn't work for allocation fastpath. In the fastpath,
> original gfp_mask is used since current_gfp_context() is introduced in
> order to control reclaim and it is on slowpath.
> Second, clearing __GFP_MOVABLE has a side effect to exclude the memory
> on the ZONE_MOVABLE for allocation target.
> 
> To fix these problems, this patch changes the implementation to exclude
> cma area in page allocation. Main point of this change is using the
> alloc_flags. alloc_flags is mainly used to control allocation so it fits
> for excluding cma area in allocation.

What are the end user visible runtime effects of this change?

This is pretty much essential information when proposing a -stable
backport.