From: Paolo Bonzini <pbonzini@redhat.com>
To: "Barret Rhoden" <brho@google.com>,
"Dan Williams" <dan.j.williams@intel.com>,
"Dave Jiang" <dave.jiang@intel.com>,
"Ross Zwisler" <zwisler@kernel.org>,
"Vishal Verma" <vishal.l.verma@intel.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>
Cc: kvm@vger.kernel.org, yu.c.zhang@intel.com,
linux-nvdimm@lists.01.org, x86@kernel.org,
linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
yi.z.zhang@intel.com
Subject: Re: [RFC PATCH] kvm: Use huge pages for DAX-backed files
Date: Tue, 6 Nov 2018 22:16:30 +0100 [thread overview]
Message-ID: <13b9a5a5-6773-131e-8014-f1b1bc975794@redhat.com> (raw)
In-Reply-To: <20181106160553.5a8025ed@gnomeregan.cam.corp.google.com>
On 06/11/2018 22:05, Barret Rhoden wrote:
> On 2018-10-29 at 17:07 Barret Rhoden <brho@google.com> wrote:
>> Another issue is that kvm_mmu_zap_collapsible_spte() also uses
>> PageTransCompoundMap() to detect huge pages, but we don't have a way to
>> get the HVA easily. Can we just aggressively zap DAX pages there?
>
> Any thoughts about this? Is there a way to determine the HVA or GFN in
> this function:
Yes, iter.gfn is the gfn inside the loop and iter.level is the level
(1=PTE, 2=PDE, ...). iter.level of course is unusable here, similar to
*levelp in transparent_hugepage_adjust, but you can use iter.gfn and
gfn_to_hva.
Paolo
> static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
> struct kvm_rmap_head *rmap_head)
> {
> u64 *sptep;
> struct rmap_iterator iter;
> int need_tlb_flush = 0;
> kvm_pfn_t pfn;
> struct kvm_mmu_page *sp;
>
> restart:
> for_each_rmap_spte(rmap_head, &iter, sptep) {
> sp = page_header(__pa(sptep));
> pfn = spte_to_pfn(*sptep);
>
> /*
> * We cannot do huge page mapping for indirect shadow pages,
> * which are found on the last rmap (level = 1) when not using
> * tdp; such shadow pages are synced with the page table in
> * the guest, and the guest page table is using 4K page size
> * mapping if the indirect sp has level = 1.
> */
> if (sp->role.direct &&
> !kvm_is_reserved_pfn(pfn) &&
> PageTransCompoundMap(pfn_to_page(pfn))) {
> pte_list_remove(rmap_head, sptep);
> need_tlb_flush = 1;
> goto restart;
> }
> }
>
> return need_tlb_flush;
> }
>
> If not, I was thinking of changing that loop to always remove PTEs for
> DAX mappings, with the understanding that they'll get faulted back in
> later. Ideally, we'd like to check if the page is huge, but DAX can't
> use the PageTransCompoundMap check.
>
> Thanks,
>
> Barret
>
>
>
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next prev parent reply other threads:[~2018-11-06 21:16 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-29 21:07 [RFC PATCH] kvm: Use huge pages for DAX-backed files Barret Rhoden
2018-10-29 22:25 ` Dan Williams
[not found] ` <CAPcyv4gJUjuSKwy7i2wuKR=Vz-AkDrxnGya5qkg7XTFxuXbtzw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-10-30 0:28 ` Barret Rhoden
2018-10-30 3:10 ` Dan Williams
[not found] ` <CAPcyv4gQztHrJ3--rhU4ZpaZyyqdqE0=gx50CRArHKiXwfYC+A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-10-30 19:45 ` Barret Rhoden
2018-10-31 8:49 ` Paolo Bonzini
2018-11-02 20:32 ` Barret Rhoden
2018-11-06 10:19 ` Paolo Bonzini
[not found] ` <876d5a71-8dda-4728-5329-4e169777ba4a-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-11-06 16:22 ` Barret Rhoden
2018-10-31 3:05 ` Yu Zhang
2018-10-31 8:52 ` Paolo Bonzini
2018-10-31 21:16 ` Dan Williams
2018-11-06 10:22 ` Paolo Bonzini
[not found] ` <20181029210716.212159-1-brho-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2018-11-06 21:05 ` Barret Rhoden
2018-11-06 21:16 ` Paolo Bonzini [this message]
2018-11-06 21:17 ` Barret Rhoden
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