linux-kernel - Re: [PATCH 06/11] mm/hugetlb: do not modify user provided gfp

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Date:   Fri, 22 May 2020 16:42:54 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@....com,
        Vlastimil Babka <vbabka@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Michal Hocko <mhocko@...e.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 06/11] mm/hugetlb: do not modify user provided gfp_mask

2020년 5월 22일 (금) 오전 7:19, Mike Kravetz <mike.kravetz@...cle.com>님이 작성:
>
> On 5/17/20 6:20 PM, js1304@...il.com wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@....com>
> >
> > It's not good practice to modify user input. Instead of using it to
> > build correct gfp_mask for APIs, this patch introduces another gfp_mask
> > field, __gfp_mask, for internal usage.
>
> Modifying the flags as is done in the existing code does not bother me
> too much, but that is just my opinion.  Adding __gfp_mask for modifications
> is fine with me if others think it is a good thing.

With the following patches, in some cases, ac->gfp_mask is set up once and
used many times. If we modify ac->gfp_mask in place, there would be side-effect.

> Does dequeue_huge_page_vma() need to be modified so that it will set
> ac.__gfp_mask before calling dequeue_huge_page_nodemask()?

Good catch! Will change!

Thanks.