linux-kernel - Re: [PATCH 1/2] mm,sparse: Fix deactivate

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Message-Id: <87wogje15a.fsf@linux.ibm.com>
Date:   Mon, 15 Jul 2019 21:32:57 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Oscar Salvador <osalvador@...e.de>, akpm@...ux-foundation.org
Cc:     dan.j.williams@...el.com, david@...hat.com,
        pasha.tatashin@...een.com, mhocko@...e.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH 1/2] mm,sparse: Fix deactivate_section for early sections

Oscar Salvador <osalvador@...e.de> writes:

> deactivate_section checks whether a section is early or not
> in order to either call free_map_bootmem() or depopulate_section_memmap().
> Being the former for sections added at boot time, and the latter for
> sections hotplugged.
>
> The problem is that we zero section_mem_map, so the last early_section()
> will always report false and the section will not be removed.
>
> Fix this checking whether a section is early or not at function
> entry.
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>

> Fixes: mmotm ("mm/sparsemem: Support sub-section hotplug")
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>  mm/sparse.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 3267c4001c6d..1e224149aab6 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -738,6 +738,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>  	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
>  	DECLARE_BITMAP(tmp, SUBSECTIONS_PER_SECTION) = { 0 };
>  	struct mem_section *ms = __pfn_to_section(pfn);
> +	bool section_is_early = early_section(ms);
>  	struct page *memmap = NULL;
>  	unsigned long *subsection_map = ms->usage
>  		? &ms->usage->subsection_map[0] : NULL;
> @@ -772,7 +773,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>  	if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION)) {
>  		unsigned long section_nr = pfn_to_section_nr(pfn);
>  
> -		if (!early_section(ms)) {
> +		if (!section_is_early) {
>  			kfree(ms->usage);
>  			ms->usage = NULL;
>  		}
> @@ -780,7 +781,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>  		ms->section_mem_map = sparse_encode_mem_map(NULL, section_nr);
>  	}
>  
> -	if (early_section(ms) && memmap)
> +	if (section_is_early && memmap)
>  		free_map_bootmem(memmap);
>  	else
>  		depopulate_section_memmap(pfn, nr_pages, altmap);
> -- 
> 2.12.3