From: Nadav Amit <namit@vmware.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>,
"jstancek@redhat.com" <jstancek@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
"Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
Nick Piggin <npiggin@gmail.com>, Minchan Kim <minchan@kernel.org>,
Mel Gorman <mgorman@suse.de>, Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] mm: mmu_gather: remove __tlb_reset_range() for force flush
Date: Mon, 13 May 2019 09:21:01 +0000 [thread overview]
Message-ID: <847D4C2F-BD26-4BE0-A5BA-3C690D11BF77@vmware.com> (raw)
In-Reply-To: <20190513091205.GO2650@hirez.programming.kicks-ass.net>
> On May 13, 2019, at 2:12 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, May 13, 2019 at 10:36:06AM +0200, Peter Zijlstra wrote:
>> On Thu, May 09, 2019 at 09:21:35PM +0000, Nadav Amit wrote:
>>> It may be possible to avoid false-positive nesting indications (when the
>>> flushes do not overlap) by creating a new struct mmu_gather_pending, with
>>> something like:
>>>
>>> struct mmu_gather_pending {
>>> u64 start;
>>> u64 end;
>>> struct mmu_gather_pending *next;
>>> }
>>>
>>> tlb_finish_mmu() would then iterate over the mm->mmu_gather_pending
>>> (pointing to the linked list) and find whether there is any overlap. This
>>> would still require synchronization (acquiring a lock when allocating and
>>> deallocating or something fancier).
>>
>> We have an interval_tree for this, and yes, that's how far I got :/
>>
>> The other thing I was thinking of is trying to detect overlap through
>> the page-tables themselves, but we have a distinct lack of storage
>> there.
>
> We might just use some state in the pmd, there's still 2 _pt_pad_[12] in
> struct page to 'use'. So we could come up with some tlb generation
> scheme that would detect conflict.
It is rather easy to come up with a scheme (and I did similar things) if you
flush the table while you hold the page-tables lock. But if you batch across
page-tables it becomes harder.
Thinking about it while typing, perhaps it is simpler than I think - if you
need to flush range that runs across more than a single table, you are very
likely to flush a range of more than 33 entries, so anyhow you are likely to
do a full TLB flush.
So perhaps just avoiding the batching if only entries from a single table
are flushed would be enough.
next prev parent reply other threads:[~2019-05-13 9:21 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-07 21:34 [PATCH] mm: mmu_gather: remove __tlb_reset_range() for force flush Yang Shi
2019-05-09 8:37 ` Will Deacon
2019-05-09 10:38 ` Peter Zijlstra
2019-05-09 10:54 ` Peter Zijlstra
2019-05-09 18:35 ` Yang Shi
2019-05-09 18:40 ` Peter Zijlstra
2019-05-09 12:44 ` Jan Stancek
2019-05-09 17:36 ` Nadav Amit
2019-05-09 18:24 ` Peter Zijlstra
2019-05-09 19:10 ` Yang Shi
2019-05-09 21:06 ` Jan Stancek
2019-05-09 21:48 ` Yang Shi
2019-05-09 22:12 ` Jan Stancek
[not found] ` <04668E51-FD87-4D53-A066-5A35ABC3A0D6@vmware.com>
[not found] ` <20190509191120.GD2623@hirez.programming.kicks-ass.net>
2019-05-09 21:21 ` Nadav Amit
2019-05-13 8:36 ` Peter Zijlstra
2019-05-13 9:11 ` Nadav Amit
2019-05-13 11:30 ` Peter Zijlstra
2019-05-13 16:37 ` Will Deacon
2019-05-13 17:06 ` Nadav Amit
2019-05-14 8:58 ` Mel Gorman
2019-05-13 9:12 ` Peter Zijlstra
2019-05-13 9:21 ` Nadav Amit [this message]
2019-05-13 11:27 ` Peter Zijlstra
2019-05-13 17:41 ` Nadav Amit
2019-05-09 18:22 ` Yang Shi
2019-05-09 19:56 ` Peter Zijlstra
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