From: Michal Hocko <mhocko@kernel.org>
To: Baoquan He <bhe@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, richardw.yang@linux.intel.com,
david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com,
rppt@linux.ibm.com, robin.murphy@arm.com
Subject: Re: [PATCH v2 4/7] mm/sparse.c: only use subsection map in VMEMMAP case
Date: Tue, 25 Feb 2020 10:57:13 +0100 [thread overview]
Message-ID: <20200225095713.GL22443@dhcp22.suse.cz> (raw)
In-Reply-To: <20200220043316.19668-5-bhe@redhat.com>
On Thu 20-02-20 12:33:13, Baoquan He wrote:
> Currently, subsection map is used when SPARSEMEM is enabled, including
> VMEMMAP case and !VMEMMAP case. However, subsection hotplug is not
> supported at all in SPARSEMEM|!VMEMMAP case, subsection map is unnecessary
> and misleading. Let's adjust code to only allow subsection map being
> used in VMEMMAP case.
This really needs more explanation I believe. What exactly happens if
somebody tries to hotremove a part of the section with !VMEMMAP? I can
see that clear_subsection_map returns 0 but that is not an error code.
Besides that section_deactivate doesn't propagate the error upwards.
/me stares into the code
OK, I can see it now. It is relying on check_pfn_span to use the proper
subsection granularity. This really begs for a comment in the code
somewhere.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
> include/linux/mmzone.h | 2 ++
> mm/sparse.c | 20 ++++++++++++++++++++
> 2 files changed, 22 insertions(+)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 462f6873905a..fc0de3a9a51e 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1185,7 +1185,9 @@ static inline unsigned long section_nr_to_pfn(unsigned long sec)
> #define SUBSECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SUBSECTION_MASK)
>
> struct mem_section_usage {
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION);
> +#endif
> /* See declaration of similar field in struct zone */
> unsigned long pageblock_flags[0];
> };
> diff --git a/mm/sparse.c b/mm/sparse.c
> index df857ee9330c..66c497d6a229 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -209,6 +209,7 @@ static inline unsigned long first_present_section_nr(void)
> return next_present_section_nr(-1);
> }
>
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> static void subsection_mask_set(unsigned long *map, unsigned long pfn,
> unsigned long nr_pages)
> {
> @@ -243,6 +244,11 @@ void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
> nr_pages -= pfns;
> }
> }
> +#else
> +void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
> +{
> +}
> +#endif
>
> /* Record a memory area against a node. */
> void __init memory_present(int nid, unsigned long start, unsigned long end)
> @@ -726,6 +732,7 @@ static void free_map_bootmem(struct page *memmap)
> }
> #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> /**
> * clear_subsection_map - Clear subsection map of one memory region
> *
> @@ -764,6 +771,12 @@ static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
>
> return 1;
> }
> +#else
> +static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> + return 0;
> +}
> +#endif
>
> static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> struct vmem_altmap *altmap)
> @@ -820,6 +833,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> ms->section_mem_map = (unsigned long)NULL;
> }
>
> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> /**
> * fill_subsection_map - fill subsection map of a memory region
> * @pfn - start pfn of the memory range
> @@ -854,6 +868,12 @@ static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
>
> return rc;
> }
> +#else
> +static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
> +{
> + return 0;
> +}
> +#endif
>
> static struct page * __meminit section_activate(int nid, unsigned long pfn,
> unsigned long nr_pages, struct vmem_altmap *altmap)
> --
> 2.17.2
>
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-02-25 9:57 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 4:33 [PATCH v2 0/7] mm/hotplug: Only use subsection map in VMEMMAP case Baoquan He
2020-02-20 4:33 ` [PATCH v2 1/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case Baoquan He
2020-02-20 6:11 ` Wei Yang
2020-02-20 12:07 ` David Hildenbrand
2020-02-26 12:31 ` David Hildenbrand
2020-02-26 13:07 ` Baoquan He
2020-02-26 18:09 ` Dan Williams
2020-03-03 8:34 ` David Hildenbrand
2020-03-03 8:39 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 2/7] mm/sparse.c: introduce new function fill_subsection_map() Baoquan He
2020-02-20 6:14 ` Wei Yang
2020-02-28 14:27 ` David Hildenbrand
2020-03-01 4:59 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 3/7] mm/sparse.c: introduce a new function clear_subsection_map() Baoquan He
2020-02-20 6:15 ` Wei Yang
2020-02-28 14:36 ` David Hildenbrand
2020-03-01 5:20 ` Baoquan He
2020-03-02 15:43 ` David Hildenbrand
2020-03-03 1:53 ` Baoquan He
2020-03-03 8:22 ` Baoquan He
2020-03-03 8:33 ` David Hildenbrand
2020-03-03 8:38 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 4/7] mm/sparse.c: only use subsection map in VMEMMAP case Baoquan He
2020-02-20 6:17 ` Wei Yang
2020-02-25 9:57 ` Michal Hocko [this message]
2020-02-26 3:53 ` Baoquan He
2020-02-26 9:10 ` Michal Hocko
2020-02-28 7:25 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 5/7] mm/sparse.c: add code comment about sub-section hotplug Baoquan He
2020-02-20 4:33 ` [PATCH v2 6/7] mm/sparse.c: move subsection_map related codes together Baoquan He
2020-02-20 6:18 ` Wei Yang
2020-02-20 7:04 ` Baoquan He
2020-02-20 7:12 ` Wei Yang
2020-02-20 8:55 ` Baoquan He
2020-02-20 21:52 ` Wei Yang
2020-02-20 4:33 ` [PATCH v2 7/7] mm/sparse.c: Use __get_free_pages() instead in populate_section_memmap() Baoquan He
2020-02-20 10:38 ` [PATCH v2 0/7] mm/hotplug: Only use subsection map in VMEMMAP case Michal Hocko
2020-02-21 14:28 ` Baoquan He
2020-02-25 9:10 ` David Hildenbrand
2020-02-25 10:02 ` Michal Hocko
2020-02-26 3:42 ` Baoquan He
2020-02-26 9:14 ` Michal Hocko
2020-02-26 12:30 ` Baoquan He
2020-02-25 10:03 ` Michal Hocko
2020-02-26 3:44 ` Baoquan He
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200225095713.GL22443@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=bhe@redhat.com \
--cc=dan.j.williams@intel.com \
--cc=david@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=osalvador@suse.de \
--cc=richardw.yang@linux.intel.com \
--cc=robin.murphy@arm.com \
--cc=rppt@linux.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).