From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@suse.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>, Oscar Salvador <osalvador@suse.de>,
Matthew Wilcox <willy@infradead.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Minchan Kim <minchan@kernel.org>, Jann Horn <jannh@google.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Dave Hansen <dave.hansen@intel.com>,
Hugh Dickins <hughd@google.com>, Rik van Riel <riel@surriel.com>,
"Michael S . Tsirkin" <mst@redhat.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Vlastimil Babka <vbabka@suse.cz>,
Richard Henderson <rth@twiddle.net>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
Matt Turner <mattst88@gmail.com>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
Helge Deller <deller@gmx.de>, Chris Zankel <chris@zankel.net>,
Max Filippov <jcmvbkbc@gmail.com>,
linux-alpha@vger.kernel.org, linux-mips@vger.kernel.org,
linux-parisc@vger.kernel.org, linux-xtensa@linux-xtensa.org,
linux-arch@vger.kernel.org
Subject: Re: [PATCH RFC] mm/madvise: introduce MADV_POPULATE to prefault/prealloc memory
Date: Fri, 19 Feb 2021 12:10:04 +0100 [thread overview]
Message-ID: <472f3bf1-595e-54e7-3022-0562cb6b3eb2@redhat.com> (raw)
In-Reply-To: <YC+bKSQdepXhqo0T@dhcp22.suse.cz>
On 19.02.21 12:04, Michal Hocko wrote:
> On Fri 19-02-21 11:43:48, David Hildenbrand wrote:
>> On 19.02.21 11:35, Michal Hocko wrote:
>>> On Wed 17-02-21 16:48:44, David Hildenbrand wrote:
>>> [...]
>>>
>>> I only got to the implementation now.
>>>
>>>> +static long madvise_populate(struct vm_area_struct *vma,
>>>> + struct vm_area_struct **prev,
>>>> + unsigned long start, unsigned long end)
>>>> +{
>>>> + struct mm_struct *mm = vma->vm_mm;
>>>> + unsigned long tmp_end;
>>>> + int locked = 1;
>>>> + long pages;
>>>> +
>>>> + *prev = vma;
>>>> +
>>>> + while (start < end) {
>>>> + /*
>>>> + * We might have temporarily dropped the lock. For example,
>>>> + * our VMA might have been split.
>>>> + */
>>>> + if (!vma || start >= vma->vm_end) {
>>>> + vma = find_vma(mm, start);
>>>> + if (!vma)
>>>> + return -ENOMEM;
>>>> + }
>>>
>>> Why do you need to find a vma when you already have one. do_madvise will
>>> give you your vma already. I do understand that you want to finish the
>>> vma for some errors but that shouldn't require handling vmas. You should
>>> be in the shope of one here unless I miss anything.
>>
>> See below, we might temporary drop the lock while not having processed all
>> pages
>>
>>>
>>>> +
>>>> + /* Bail out on incompatible VMA types. */
>>>> + if (vma->vm_flags & (VM_IO | VM_PFNMAP) ||
>>>> + !vma_is_accessible(vma)) {
>>>> + return -EINVAL;
>>>> + }
>>>> +
>>>> + /*
>>>> + * Populate pages and take care of VM_LOCKED: simulate user
>>>> + * space access.
>>>> + *
>>>> + * For private, writable mappings, trigger a write fault to
>>>> + * break COW (i.e., shared zeropage). For other mappings (i.e.,
>>>> + * read-only, shared), trigger a read fault.
>>>> + */
>>>> + tmp_end = min_t(unsigned long, end, vma->vm_end);
>>>> + pages = populate_vma_page_range(vma, start, tmp_end, &locked);
>>>> + if (!locked) {
>>>> + mmap_read_lock(mm);
>>>> + *prev = NULL;
>>>> + vma = NULL;
>>
>> ^ here
>>
>> so, the VMA might have been replaced/split/... in the meantime.
>>
>> So to make forward progress, I have to lookup again. (similar. but different
>> to madvise_dontneed_free()).
>
> Right. Missed that.
It would look more natural if we'd just be processing the whole range -
but then it would not fit into the generic infrastructure and would
result in even more code.
I decided to go with "process the passed range and treat the given VMA
as an initial VMA that is invalidated as soon as we drop the lock".
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-02-19 11:10 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 15:48 [PATCH RFC] mm/madvise: introduce MADV_POPULATE to prefault/prealloc memory David Hildenbrand
2021-02-17 16:46 ` Dave Hansen
2021-02-17 17:06 ` David Hildenbrand
2021-02-17 17:21 ` Vlastimil Babka
2021-02-18 11:07 ` Rolf Eike Beer
2021-02-18 11:27 ` David Hildenbrand
2021-02-18 10:25 ` Michal Hocko
2021-02-18 10:44 ` David Hildenbrand
2021-02-18 10:54 ` David Hildenbrand
2021-02-18 11:28 ` Michal Hocko
2021-02-18 11:27 ` Michal Hocko
2021-02-18 11:38 ` David Hildenbrand
2021-02-18 12:22 ` [PATCH RFC] madvise.2: Document MADV_POPULATE David Hildenbrand
2021-02-18 22:59 ` [PATCH RFC] mm/madvise: introduce MADV_POPULATE to prefault/prealloc memory Peter Xu
2021-02-19 8:20 ` David Hildenbrand
2021-02-19 16:31 ` Peter Xu
2021-02-19 17:13 ` David Hildenbrand
2021-02-19 19:14 ` David Hildenbrand
2021-02-19 19:25 ` Mike Kravetz
2021-02-20 9:01 ` David Hildenbrand
2021-02-19 19:23 ` Peter Xu
2021-02-19 20:04 ` David Hildenbrand
2021-02-22 12:46 ` Michal Hocko
2021-02-22 12:52 ` David Hildenbrand
2021-02-19 10:35 ` Michal Hocko
2021-02-19 10:43 ` David Hildenbrand
2021-02-19 11:04 ` Michal Hocko
2021-02-19 11:10 ` David Hildenbrand [this message]
2021-02-20 9:12 ` David Hildenbrand
2021-02-22 12:56 ` Michal Hocko
2021-02-22 12:59 ` David Hildenbrand
2021-02-22 13:19 ` Michal Hocko
2021-02-22 13:22 ` David Hildenbrand
2021-02-22 14:02 ` Michal Hocko
2021-02-22 15:30 ` David Hildenbrand
2021-02-24 14:25 ` David Hildenbrand
2021-02-24 14:38 ` David Hildenbrand
2021-02-25 8:41 ` David Hildenbrand
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