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Groups > linux.kernel > #1736268
| From | Dave Hansen <dave.hansen@intel.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) |
| Date | 2017-09-21 01:50 +0200 |
| Message-ID | <urWUG-1nO-9@gated-at.bofh.it> (permalink) |
| References | (3 earlier) <uoylP-4IG-1@gated-at.bofh.it> <uozrA-5Ep-27@gated-at.bofh.it> <uoOqB-7dv-5@gated-at.bofh.it> <uoUw2-2qj-9@gated-at.bofh.it> <uoXWW-4LY-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 09/12/2017 11:13 AM, Tycho Andersen wrote:
> -void xpfo_alloc_pages(struct page *page, int order, gfp_t gfp)
> +void xpfo_alloc_pages(struct page *page, int order, gfp_t gfp, bool will_map)
> {
> int i, flush_tlb = 0;
> struct xpfo *xpfo;
> @@ -116,8 +116,14 @@ void xpfo_alloc_pages(struct page *page, int order, gfp_t gfp)
> * Tag the page as a user page and flush the TLB if it
> * was previously allocated to the kernel.
> */
> - if (!test_and_set_bit(XPFO_PAGE_USER, &xpfo->flags))
> + bool was_user = !test_and_set_bit(XPFO_PAGE_USER,
> + &xpfo->flags);
> +
> + if (was_user || !will_map) {
> + set_kpte(page_address(page + i), page + i,
> + __pgprot(0));
> flush_tlb = 1;
> + }
Shouldn't the "was_user" be "was_kernel"?
Also, the way this now works, let's say we have a nice, 2MB pmd_t (page
table entry) mapping a nice, 2MB page in the allocator. Then it gets
allocated to userspace. We do
for (i = 0; i < (1 << order); i++) {
...
set_kpte(page_address(page + i), page+i, __pgprot(0));
}
The set_kpte() will take the nice, 2MB mapping and break it down into
512 4k mappings, all pointing to a non-present PTE, in a newly-allocated
PTE page. So, you get the same result and waste 4k of memory in the
process, *AND* make it slower because we added a level to the page tables.
I think you actually want to make a single set_kpte() call at the end of
the function. That's faster and preserves the large page in the direct
mapping.
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Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Yisheng Xie <xieyisheng1@huawei.com> - 2017-09-11 09:30 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Tycho Andersen <tycho@docker.com> - 2017-09-11 17:00 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Juerg Haefliger <juerg.haefliger@canonical.com> - 2017-09-11 18:10 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Tycho Andersen <tycho@docker.com> - 2017-09-11 19:00 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Yisheng Xie <xieyisheng1@huawei.com> - 2017-09-12 10:10 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Tycho Andersen <tycho@docker.com> - 2017-09-12 16:40 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Tycho Andersen <tycho@docker.com> - 2017-09-12 20:20 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Yisheng Xie <xieyisheng1@huawei.com> - 2017-09-14 08:20 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Dave Hansen <dave.hansen@intel.com> - 2017-09-21 01:50 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Dave Hansen <dave.hansen@intel.com> - 2017-09-21 02:10 +0200
Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) Tycho Andersen <tycho@docker.com> - 2017-09-21 02:10 +0200
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