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Tue, 3 Mar 2020 08:38:24 +0000 (UTC) Received: from localhost (ovpn-12-29.pek2.redhat.com [10.72.12.29]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2B32A60BF3; Tue, 3 Mar 2020 08:38:21 +0000 (UTC) Date: Tue, 3 Mar 2020 16:38:18 +0800 From: Baoquan He To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, richardw.yang@linux.intel.com, osalvador@suse.de, dan.j.williams@intel.com, mhocko@suse.com, rppt@linux.ibm.com, robin.murphy@arm.com Subject: Re: [PATCH v2 3/7] mm/sparse.c: introduce a new function clear_subsection_map() Message-ID: <20200303083818.GB4433@MiWiFi-R3L-srv> References: <20200220043316.19668-1-bhe@redhat.com> <20200220043316.19668-4-bhe@redhat.com> <20200301052028.GN24216@MiWiFi-R3L-srv> <1346f0c2-7b1f-6feb-5e9b-2854fd0022ba@redhat.com> <20200303082204.GA4433@MiWiFi-R3L-srv> <53bba557-149c-54b5-c8d7-27f7b6a55eb0@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53bba557-149c-54b5-c8d7-27f7b6a55eb0@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > >>>>> --- > >>>>> 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) { > ... > }