linux-kernel - Re: [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable

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Message-Id: <6A58E80B-7A5F-4CAD-ACF1-89BCCBE4D3B1@lca.pw>
Date:   Thu, 3 Oct 2019 08:14:40 -0400
From:   Qian Cai <cai@....pw>
To:     Anshuman Khandual <Anshuman.Khandual@....com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Oscar Salvador <osalvador@...e.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable_pages()



> On Oct 3, 2019, at 8:01 AM, Anshuman Khandual <Anshuman.Khandual@....com> wrote:
> 
> Will something like this be better ?

Not really. dump_page() will dump PageCompound information anyway, so it is trivial to figure out if went in that path.

> hugepage_migration_supported() has got
> uncertainty depending on platform and huge page size.
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 15c2050c629b..8dbc86696515 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8175,7 +8175,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>        unsigned long found;
>        unsigned long iter = 0;
>        unsigned long pfn = page_to_pfn(page);
> -       const char *reason = "unmovable page";
> +       const char *reason;
> 
>        /*
>         * TODO we could make this much more efficient by not checking every
> @@ -8194,7 +8194,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>                if (is_migrate_cma(migratetype))
>                        return false;
> 
> -               reason = "CMA page";
> +               reason = "Unmovable CMA page";
>                goto unmovable;
>        }
> 
> @@ -8206,8 +8206,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> 
>                page = pfn_to_page(check);
> 
> -               if (PageReserved(page))
> +               if (PageReserved(page)) {
> +                       reason = "Unmovable reserved page";
>                        goto unmovable;
> +               }
> 
>                /*
>                 * If the zone is movable and we have ruled out all reserved
> @@ -8226,8 +8228,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>                        struct page *head = compound_head(page);
>                        unsigned int skip_pages;
> 
> -                       if (!hugepage_migration_supported(page_hstate(head)))
> +                       if (!hugepage_migration_supported(page_hstate(head))) {
> +                               reason = "Unmovable HugeTLB page";
>                                goto unmovable;
> +                       }
> 
>                        skip_pages = compound_nr(head) - (page - head);
>                        iter += skip_pages - 1;
> @@ -8271,8 +8275,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>                 * is set to both of a memory hole page and a _used_ kernel
>                 * page at boot.
>                 */
> -               if (found > count)
> +               if (found > count) {
> +                       reason = "Unmovable non-LRU page";
>                        goto unmovable;
> +               }
>        }
>        return false;
> unmovable: