From: Muchun Song <songmuchun@bytedance.com>
To: Mike Kravetz <mike.kravetz@oracle.com>,
Oscar Salvador <osalvador@suse.de>
Cc: Jonathan Corbet <corbet@lwn.net>,
Thomas Gleixner <tglx@linutronix.de>,
mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
dave.hansen@linux.intel.com, luto@kernel.org,
Peter Zijlstra <peterz@infradead.org>,
viro@zeniv.linux.org.uk,
Andrew Morton <akpm@linux-foundation.org>,
paulmck@kernel.org, mchehab+huawei@kernel.org,
pawan.kumar.gupta@linux.intel.com,
Randy Dunlap <rdunlap@infradead.org>,
oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de,
Mina Almasry <almasrymina@google.com>,
David Rientjes <rientjes@google.com>,
Matthew Wilcox <willy@infradead.org>,
Michal Hocko <mhocko@suse.com>,
"Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
David Hildenbrand <david@redhat.com>,
Xiongchun duan <duanxiongchun@bytedance.com>,
linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
Linux Memory Management List <linux-mm@kvack.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [External] Re: [PATCH v9 03/11] mm/hugetlb: Free the vmemmap pages associated with each HugeTLB page
Date: Thu, 17 Dec 2020 14:54:10 +0800 [thread overview]
Message-ID: <CAMZfGtXwU7LcTZw7iKFNksVTYx8Bhd=9Nct+zfNy_ibuFiF6ew@mail.gmail.com> (raw)
In-Reply-To: <49f6a0f1-c6fa-4642-2db0-69f090e8a392@oracle.com>
On Thu, Dec 17, 2020 at 6:52 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 12/16/20 2:25 PM, Oscar Salvador wrote:
> > On Wed, Dec 16, 2020 at 02:08:30PM -0800, Mike Kravetz wrote:
> >>> + * vmemmap_rmap_walk - walk vmemmap page table
> >>> +
> >>> +static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
> >>> + unsigned long end, struct vmemmap_rmap_walk *walk)
> >>> +{
> >>> + pte_t *pte;
> >>> +
> >>> + pte = pte_offset_kernel(pmd, addr);
> >>> + do {
> >>> + BUG_ON(pte_none(*pte));
> >>> +
> >>> + if (!walk->reuse)
> >>> + walk->reuse = pte_page(pte[VMEMMAP_TAIL_PAGE_REUSE]);
> >>
> >> It may be just me, but I don't like the pte[-1] here. It certainly does work
> >> as designed because we want to remap all pages in the range to the page before
> >> the range (at offset -1). But, we do not really validate this 'reuse' page.
> >> There is the BUG_ON(pte_none(*pte)) as a sanity check, but we do nothing similar
> >> for pte[-1]. Based on the usage for HugeTLB pages, we can be confident that
> >> pte[-1] is actually a pte. In discussions with Oscar, you mentioned another
> >> possible use for these routines.
> >
> > Without giving it much of a thought, I guess we could duplicate the
> > BUG_ON for the pte outside the loop, and add a new one for pte[-1].
> > Also, since walk->reuse seems to not change once it is set, we can take
> > it outside the loop? e.g:
> >
> > pte *pte;
> >
> > pte = pte_offset_kernel(pmd, addr);
> > BUG_ON(pte_none(*pte));
> > BUG_ON(pte_none(pte[VMEMMAP_TAIL_PAGE_REUSE]));
> > walk->reuse = pte_page(pte[VMEMMAP_TAIL_PAGE_REUSE]);
> > do {
> > ....
> > } while...
> >
> > Or I am not sure whether we want to keep it inside the loop in case
> > future cases change walk->reuse during the operation.
> > But to be honest, I do not think it is realistic of all future possible
> > uses of this, so I would rather keep it simple for now.
>
> I was thinking about possibly passing the 'reuse' address as another parameter
> to vmemmap_remap_reuse(). We could add this addr to the vmemmap_rmap_walk
> struct and set walk->reuse when we get to the pte for that address. Of
> course this would imply that the addr would need to be part of the range.
Maybe adding another one parameter is unnecessary. How about doing
this in the vmemmap_remap_reuse?
The 'reuse' address just is start + PAGE_SIZE.
void vmemmap_remap_free(unsigned long start, unsigned long size)
{
unsigned long end = start + size;
unsigned long reuse_addr = start + PAGE_SIZE;
LIST_HEAD(vmemmap_pages);
struct vmemmap_remap_walk walk = {
.remap_pte = vmemmap_remap_pte,
.vmemmap_pages = &vmemmap_pages,
.reuse_addr = reuse_addr.
};
}
>
> Ideally, we would walk the page table to get to the reuse page. My concern
> was not explicitly about adding the BUG_ON. In more general use, *pte could
> be the first entry on a pte page. And, then pte[-1] may not even be a pte.
>
> Again, I don't think this matters for the current HugeTLB use case. Just a
> little concerned if code is put to use for other purposes.
> --
> Mike Kravetz
--
Yours,
Muchun
next prev parent reply other threads:[~2020-12-17 6:54 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-13 15:45 [PATCH v9 00/11] Free some vmemmap pages of HugeTLB page Muchun Song
2020-12-13 15:45 ` [PATCH v9 01/11] mm/memory_hotplug: Factor out bootmem core functions to bootmem_info.c Muchun Song
2020-12-13 15:45 ` [PATCH v9 02/11] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2020-12-16 1:03 ` Mike Kravetz
2020-12-16 3:24 ` [External] " Muchun Song
2020-12-16 3:45 ` Mike Kravetz
2020-12-16 3:52 ` [External] " Muchun Song
2020-12-13 15:45 ` [PATCH v9 03/11] mm/hugetlb: Free the vmemmap pages associated with each HugeTLB page Muchun Song
2020-12-16 13:06 ` Oscar Salvador
2020-12-16 13:15 ` [External] " Muchun Song
2020-12-16 22:08 ` Mike Kravetz
2020-12-16 22:25 ` Oscar Salvador
2020-12-16 22:49 ` Mike Kravetz
2020-12-17 6:54 ` Muchun Song [this message]
2020-12-17 9:05 ` [External] " Muchun Song
2020-12-17 4:06 ` Muchun Song
2020-12-13 15:45 ` [PATCH v9 04/11] mm/hugetlb: Defer freeing of HugeTLB pages Muchun Song
2020-12-16 23:48 ` Mike Kravetz
2020-12-17 3:19 ` [External] " Muchun Song
2020-12-13 15:45 ` [PATCH v9 05/11] mm/hugetlb: Allocate the vmemmap pages associated with each HugeTLB page Muchun Song
2020-12-17 1:17 ` Mike Kravetz
2020-12-17 3:22 ` [External] " Muchun Song
2020-12-13 15:45 ` [PATCH v9 06/11] mm/hugetlb: Set the PageHWPoison to the raw error page Muchun Song
2020-12-16 13:28 ` Oscar Salvador
2020-12-16 13:51 ` [External] " Muchun Song
2020-12-16 13:30 ` Oscar Salvador
2020-12-13 15:45 ` [PATCH v9 07/11] mm/hugetlb: Flush work when dissolving hugetlb page Muchun Song
2020-12-13 15:45 ` [PATCH v9 08/11] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
2020-12-16 14:40 ` Oscar Salvador
2020-12-16 16:04 ` [External] " Muchun Song
2020-12-16 22:10 ` Oscar Salvador
2020-12-17 2:45 ` Muchun Song
2020-12-13 15:45 ` [PATCH v9 09/11] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2020-12-16 13:43 ` Oscar Salvador
2020-12-16 13:56 ` [External] " Muchun Song
2020-12-16 22:12 ` Oscar Salvador
2020-12-17 8:34 ` Muchun Song
2020-12-13 15:45 ` [PATCH v9 10/11] mm/hugetlb: Gather discrete indexes of tail page Muchun Song
2020-12-16 14:03 ` Oscar Salvador
2020-12-16 14:26 ` [External] " Muchun Song
2020-12-13 15:45 ` [PATCH v9 11/11] mm/hugetlb: Optimize the code with the help of the compiler Muchun Song
2020-12-17 10:31 ` Oscar Salvador
2020-12-17 10:42 ` [External] " Muchun Song
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