linux-kernel - Re: [PATCH v2 00/12] clean-up the migration target allocation functions

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Date:   Thu, 28 May 2020 21:25:02 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@....com, 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>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 00/12] clean-up the migration target allocation
 functions

On 5/27/20 8:44 AM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> This patchset clean-up the migration target allocation functions.
> 
> * Changes on v2
> - add acked-by tags
> - fix missing compound_head() call for the patch #3
> - remove thisnode field on alloc_control and use __GFP_THISNODE directly
> - fix missing __gfp_mask setup for the patch
> "mm/hugetlb: do not modify user provided gfp_mask"
> 
> * Cover-letter
> 
> Contributions of this patchset are:
> 1. unify two hugetlb alloc functions. As a result, one is remained.
> 2. make one external hugetlb alloc function to internal one.
> 3. unify three functions for migration target allocation.
> 
> The patchset is based on next-20200526.
> The patchset is available on:

I went through the series and I'd like to make some high-level suggestions
first, that should hopefully simplify the code a bit more and reduce churn:

- in the series, alloc_huge_page_nodemask() becomes the only caller of
alloc_migrate_huge_page(). So you can inline the code there, and it's one less
function out of many with similar name :)

- after that, alloc_huge_page_nodemask(ac) uses ac mostly just to extract
individual fields, and only pass it as a whole to dequeue_huge_page_nodemask().
The only other caller of dequeue...() is dequeue_huge_page_vma() who has to
construct ac from scratch. It might be probably simpler not to introduce struct
alloc_control into hugetlb code at all, and only keep it for
alloc_migrate_target(), at which point it can have a more specific name as
discussed and there's less churn

- I'd suggest not change signature of migrate_pages(), free_page_t and
new_page_t, keeping the opaque private field is fine as not all callbacks use
struct alloc_context pointer, and then e.g. compaction_alloc has to use the
private field etc. alloc_migration_target() can simply cast the private to
struct alloc_control *ac as the first thing

Thanks!
Vlastimil

> https://github.com/JoonsooKim/linux/tree/cleanup-migration-target-allocation-v2.00-next-20200526
> 
> Thanks.
> 
> Joonsoo Kim (12):
>   mm/page_isolation: prefer the node of the source page
>   mm/migrate: move migration helper from .h to .c
>   mm/hugetlb: introduce alloc_control structure to simplify migration
>     target allocation APIs
>   mm/hugetlb: use provided ac->gfp_mask for allocation
>   mm/hugetlb: unify hugetlb migration callback function
>   mm/hugetlb: make hugetlb migration target allocation APIs CMA aware
>   mm/hugetlb: do not modify user provided gfp_mask
>   mm/migrate: change the interface of the migration target alloc/free
>     functions
>   mm/migrate: make standard migration target allocation functions
>   mm/gup: use standard migration target allocation function
>   mm/mempolicy: use standard migration target allocation function
>   mm/page_alloc: use standard migration target allocation function
>     directly
> 
>  include/linux/hugetlb.h        | 33 ++++++---------
>  include/linux/migrate.h        | 44 +++++---------------
>  include/linux/page-isolation.h |  4 +-
>  mm/compaction.c                | 15 ++++---
>  mm/gup.c                       | 60 +++++-----------------------
>  mm/hugetlb.c                   | 91 ++++++++++++++++++++----------------------
>  mm/internal.h                  | 12 +++++-
>  mm/memory-failure.c            | 14 ++++---
>  mm/memory_hotplug.c            | 10 +++--
>  mm/mempolicy.c                 | 38 ++++++------------
>  mm/migrate.c                   | 72 +++++++++++++++++++++++++--------
>  mm/page_alloc.c                |  9 ++++-
>  mm/page_isolation.c            |  5 ---
>  13 files changed, 191 insertions(+), 216 deletions(-)
>