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From: Vlastimil Babka <vbabka@suse.cz>
To: Mike Rapoport <rppt@kernel.org>, Dave Hansen <dave.hansen@intel.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Ira Weiny <ira.weiny@intel.com>,
	Kees Cook <keescook@chromium.org>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 4/4] x86/mm: write protect (most) page tables
Date: Thu, 26 Aug 2021 11:01:18 +0200	[thread overview]
Message-ID: <de31a1c7-1a35-831f-3eed-e4a6e77f9e44@suse.cz> (raw)
In-Reply-To: <YSdKsTX3EQQqgj0y@kernel.org>

On 8/26/21 10:02, Mike Rapoport wrote:
> On Mon, Aug 23, 2021 at 04:50:10PM -0700, Dave Hansen wrote:
>> On 8/23/21 6:25 AM, Mike Rapoport wrote:
>> >  void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte)
>> >  {
>> > +	enable_pgtable_write(page_address(pte));
>> >  	pgtable_pte_page_dtor(pte);
>> >  	paravirt_release_pte(page_to_pfn(pte));
>> >  	paravirt_tlb_remove_table(tlb, pte);
>> > @@ -69,6 +73,7 @@ void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
>> >  #ifdef CONFIG_X86_PAE
>> >  	tlb->need_flush_all = 1;
>> >  #endif
>> > +	enable_pgtable_write(pmd);
>> >  	pgtable_pmd_page_dtor(page);
>> >  	paravirt_tlb_remove_table(tlb, page);
>> >  }
>> 
>> I'm also cringing a bit at hacking this into the page allocator.   A
>> *lot* of what you're trying to do with getting large allocations out and
>> splitting them up is done very well today by the slab allocators.  It
>> might take some rearrangement of 'struct page' metadata to be more slab
>> friendly, but it does seem like a close enough fit to warrant investigating.
> 
> I thought more about using slab, but it seems to me the least suitable
> option. The usecases at hand (page tables, secretmem, SEV/TDX) allocate in
> page granularity and some of them use struct page metadata, so even its
> rearrangement won't help. And adding support for 2M slabs to SLUB would be
> quite intrusive.

Agree, and there would be unnecessary memory overhead too, SLUB would be happy
to cache a 2MB block on each CPU, etc.

> I think that better options are moving such cache deeper into buddy or
> using e.g. genalloc instead of a list to deal with higher order allocations. 
> 
> The choice between these two will mostly depend of the API selection, i.e.
> a GFP flag or a dedicated alloc/free.

Implementing on top of buddy seem still like the better option to me.

  reply	other threads:[~2021-08-26  9:01 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-23 13:25 [RFC PATCH 0/4] mm/page_alloc: cache pte-mapped allocations Mike Rapoport
2021-08-23 13:25 ` [RFC PATCH 1/4] list: Support getting most recent element in list_lru Mike Rapoport
2021-08-23 13:25 ` [RFC PATCH 2/4] list: Support list head not in object for list_lru Mike Rapoport
2021-08-23 13:25 ` [RFC PATCH 3/4] mm/page_alloc: introduce __GFP_PTE_MAPPED flag to allocate pte-mapped pages Mike Rapoport
2021-08-23 20:29   ` Edgecombe, Rick P
2021-08-24 13:02     ` Mike Rapoport
2021-08-24 16:38       ` Edgecombe, Rick P
2021-08-24 16:54         ` Mike Rapoport
2021-08-24 17:23           ` Edgecombe, Rick P
2021-08-24 17:37             ` Mike Rapoport
2021-08-24 16:12   ` Vlastimil Babka
2021-08-25  8:43   ` David Hildenbrand
2021-08-23 13:25 ` [RFC PATCH 4/4] x86/mm: write protect (most) page tables Mike Rapoport
2021-08-23 20:08   ` Edgecombe, Rick P
2021-08-23 23:50   ` Dave Hansen
2021-08-24  3:34     ` Andy Lutomirski
2021-08-25 14:59       ` Dave Hansen
2021-08-24 13:32     ` Mike Rapoport
2021-08-25  8:38     ` David Hildenbrand
2021-08-26  8:02     ` Mike Rapoport
2021-08-26  9:01       ` Vlastimil Babka [this message]
     [not found]   ` <FB6C09CD-9CEA-4FE8-B179-98DB63EBDD68@gmail.com>
2021-08-24  5:34     ` Nadav Amit
2021-08-24 13:36       ` Mike Rapoport
2021-08-23 20:02 ` [RFC PATCH 0/4] mm/page_alloc: cache pte-mapped allocations Edgecombe, Rick P
2021-08-24 13:03   ` Mike Rapoport
2021-08-24 16:09 ` Vlastimil Babka
2021-08-29  7:06   ` Mike Rapoport

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