linux-kernel - Re: [PATCH 0/8] implement "memmap on memory" feature on s390

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Message-ID: <920bb896-ee9e-4124-a4fc-f22d1439c95b@redhat.com>
Date:   Tue, 21 Nov 2023 15:42:43 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Sumanth Korikkar <sumanthk@...ux.ibm.com>
Cc:     Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/8] implement "memmap on memory" feature on s390

On 21.11.23 14:21, Sumanth Korikkar wrote:
> On Tue, Nov 21, 2023 at 02:13:22PM +0100, Sumanth Korikkar wrote:
>> Approach 2:
>> ===========
>> Shouldnt kasan zero shadow mapping performed first before
>> accessing/initializing memmap via page_init_poisining()?  If that is
>> true, then it is a problem for all architectures and should could be
>> fixed like:
>>
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 7a5fc89a8652..eb3975740537 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1093,6 +1093,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
>>   	if (ret)
>>   		return ret;
>>
>> +	page_init_poison(pfn_to_page(pfn), sizeof(struct page) * nr_pages);
>>   	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE);
>>
>>   	for (i = 0; i < nr_pages; i++)
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index 77d91e565045..4ddf53f52075 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -906,8 +906,11 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>>   	/*
>>   	 * Poison uninitialized struct pages in order to catch invalid flags
>>   	 * combinations.
>> +	 * For altmap, do this later when onlining the memory, as it might
>> +	 * not be accessible at this point.
>>   	 */
>> -	page_init_poison(memmap, sizeof(struct page) * nr_pages);
>> +	if (!altmap)
>> +		page_init_poison(memmap, sizeof(struct page) * nr_pages);
>>
>>   	ms = __nr_to_section(section_nr);
>>   	set_section_nid(section_nr, nid);
>>
>>
>>
>> Also, if this approach is taken, should page_init_poison() be performed
>> with cond_resched() as mentioned in commit d33695b16a9f
>> ("mm/memory_hotplug: poison memmap in remove_pfn_range_from_zone()") ?
> 
> Sorry, wrong commit id.
> 
> should page_init_poison() be performed with cond_resched() as mentioned in
> Commit b7e3debdd040 ("mm/memory_hotplug.c: fix false softlockup
> during pfn range removal") ?

I think people are currently looking into removing all that cond_resched():

https://lore.kernel.org/all/20231107230822.371443-29-ankur.a.arora@oracle.com/T/#mda52da685a142bec9607625386b0b660e5470abe
-- 
Cheers,

David / dhildenb