linux-kernel - Re: [PATCH 2/7] mm/sparse.c: Introduce a new function clear_subsection

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Date:   Mon, 10 Feb 2020 11:36:27 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, dan.j.williams@...el.com,
        david@...hat.com
Subject: Re: [PATCH 2/7] mm/sparse.c: Introduce a new function
 clear_subsection_map()

On 02/10/20 at 07:07am, Wei Yang wrote:
> On Sun, Feb 09, 2020 at 06:48:21PM +0800, Baoquan He wrote:
> >Wrap the codes clearing subsection map of one memory region in
> >section_deactivate() into clear_subsection_map().
> >
> 
> Patch 1 and 2 server the same purpose -- to #ifdef the VMEMMAP.

Hmm, I didn't say patch 1 and 2 are preparation works because they had
better be done even if we don't take off subsection map from
SPARSEMEM|!VMEMMAP case. Wrapping the subsection map filling and clearing
codes into separate new functions, can make section_activate() and
section_deactivate() much clearer on code logic.

If you don't mind, I will keep them for now, and see what other people
will say.

Thanks
Baoquan

> 
> >---
> > mm/sparse.c | 44 +++++++++++++++++++++++++++++++++++++-------
> > 1 file changed, 37 insertions(+), 7 deletions(-)
> >
> >diff --git a/mm/sparse.c b/mm/sparse.c
> >index 9ad741ccbeb6..696f6b9f706e 100644
> >--- a/mm/sparse.c
> >+++ b/mm/sparse.c
> >@@ -726,14 +726,25 @@ static void free_map_bootmem(struct page *memmap)
> > }
> > #endif /* CONFIG_SPARSEMEM_VMEMMAP */
> > 
> >-static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> >-		struct vmem_altmap *altmap)
> >+/**
> >+ * clear_subsection_map - Clear subsection map of one memory region
> >+ *
> >+ * @pfn - start pfn of the memory range
> >+ * @nr_pages - number of pfns to add in the region
> >+ *
> >+ * This is only intended for hotplug, and clear the related subsection
> >+ * map inside one section.
> >+ *
> >+ * Return:
> >+ * * -EINVAL	- Section already deactived.
> >+ * * 0		- Subsection map is emptied.
> >+ * * 1		- Subsection map is not empty.
> >+ */
> >+static int clear_subsection_map(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;
> > 
> >@@ -744,8 +755,28 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> > 	if (WARN(!subsection_map || !bitmap_equal(tmp, map, SUBSECTIONS_PER_SECTION),
> > 				"section already deactivated (%#lx + %ld)\n",
> > 				pfn, nr_pages))
> >-		return;
> >+		return -EINVAL;
> >+
> >+	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> > 
> >+	if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> >+		return 0;
> >+
> >+	return 1;
> >+}
> >+
> >+static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> >+		struct vmem_altmap *altmap)
> >+{
> >+	struct mem_section *ms = __pfn_to_section(pfn);
> >+	bool section_is_early = early_section(ms);
> >+	struct page *memmap = NULL;
> >+	int rc;
> >+
> >+
> >+	rc = clear_subsection_map(pfn, nr_pages);
> >+	if(IS_ERR_VALUE((unsigned long)rc))
> >+		return;
> > 	/*
> > 	 * There are 3 cases to handle across two configurations
> > 	 * (SPARSEMEM_VMEMMAP={y,n}):
> >@@ -763,8 +794,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> > 	 *
> > 	 * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified
> > 	 */
> >-	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> >-	if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION)) {
> >+	if (!rc) {
> > 		unsigned long section_nr = pfn_to_section_nr(pfn);
> > 
> > 		/*
> >-- 
> >2.17.2
> 
> -- 
> Wei Yang
> Help you, Help me
>