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Date: Tue, 3 Mar 2020 16:38:18 +0800
From: Baoquan He <bhe@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
akpm@...ux-foundation.org, richardw.yang@...ux.intel.com,
osalvador@...e.de, dan.j.williams@...el.com, mhocko@...e.com,
rppt@...ux.ibm.com, robin.murphy@....com
Subject: Re: [PATCH v2 3/7] mm/sparse.c: introduce a new function
clear_subsection_map()
On 03/03/20 at 09:33am, David Hildenbrand wrote:
> On 03.03.20 09:22, Baoquan He wrote:
> > On 03/02/20 at 04:43pm, David Hildenbrand wrote:
> >> On 01.03.20 06:20, Baoquan He wrote:
> >>> On 02/28/20 at 03:36pm, David Hildenbrand wrote:
> >>>> On 20.02.20 05:33, Baoquan He wrote:
> >>>>> Wrap the codes which clear subsection map of one memory region from
> >>>>> section_deactivate() into clear_subsection_map().
> >>>>>
> >>>>> Signed-off-by: Baoquan He <bhe@...hat.com>
> >>>>> ---
> >>>>> mm/sparse.c | 46 ++++++++++++++++++++++++++++++++++++++--------
> >>>>> 1 file changed, 38 insertions(+), 8 deletions(-)
> >>>>>
> >>>>> diff --git a/mm/sparse.c b/mm/sparse.c
> >>>>> index 977b47acd38d..df857ee9330c 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.
> >>>>> + */
> >>>>
> >>>> Less verbose please (in my preference: none and simplify return handling)
> >>>>
> >>>>> +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;
> >>>>> +
> >>>>
> >>>> Can we please just have a
> >>>>
> >>>> subsection_map_empty() instead and handle that in the caller?
> >>>> (you can then always return true in the !VMEMMAP variant)
> >>>
> >>> I don't follow. Could you be more specific? or pseudo code please?
> >>>
> >>> The old code has to handle below case in which subsection_map has been
> >>> cleared. And I introduce clear_subsection_map() to encapsulate all
> >>> subsection map realted code so that !VMEMMAP won't have to see it any
> >>> more.
> >>>
> >>
> >> Something like this on top would be easier to understand IMHO
> >>
> >>
> >> diff --git a/mm/sparse.c b/mm/sparse.c
> >> index dc79b00ddaaa..be5c80e9cfee 100644
> >> --- a/mm/sparse.c
> >> +++ b/mm/sparse.c
> >> @@ -726,20 +726,6 @@ static void free_map_bootmem(struct page *memmap)
> >> }
> >> #endif /* CONFIG_SPARSEMEM_VMEMMAP */
> >>
> >> -/**
> >> - * 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 };
> >> @@ -758,11 +744,12 @@ static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
> >> return -EINVAL;
> >>
> >> bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> >> + return 0;
> >> +}
> >>
> >> - if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> >> - return 0;
> >> -
> >> - return 1;
> >> +static bool is_subsection_map_empty(unsigned long pfn, unsigned long nr_pages)
> >> +{
> >> + return bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION);
> >> }
> >>
> >> static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> >> @@ -771,11 +758,8 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> >> 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))
> >> + if (unlikely(clear_subsection_map(pfn, nr_pages)))
> >> return;
> >> /*
> >> * There are 3 cases to handle across two configurations
> >> @@ -794,7 +778,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> >> *
> >> * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified
> >> */
> >> - if (!rc) {
> >> + if (is_subsection_map_empty(pfn, nr_pages)) {
> >> unsigned long section_nr = pfn_to_section_nr(pfn);
> >
> > Tried this way, it's not good in this patch. Since ms->usage might be
> > freed in this place.
> >
> > if (!PageReserved(virt_to_page(ms->usage))) {
> > kfree(ms->usage);
> > ms->usage = NULL;
> > }
>
> So your patch #1 is already broken. Just cache the result in patch #1.
>
> bool empty;
Right, good catch. Will take this way. Thanks.
>
> ...
> empty = bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION);
> ...
> if (empty) {
> ...
> }
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