From: David Hildenbrand <david@redhat.com>
To: SeongJae Park <sjpark@amazon.com>
Cc: akpm@linux-foundation.org, SeongJae Park <sjpark@amazon.de>,
Jonathan.Cameron@Huawei.com, aarcange@redhat.com,
acme@kernel.org, alexander.shishkin@linux.intel.com,
amit@kernel.org, benh@kernel.crashing.org,
brendan.d.gregg@gmail.com, brendanhiggins@google.com, cai@lca.pw,
colin.king@canonical.com, corbet@lwn.net, dwmw@amazon.com,
foersleo@amazon.de, irogers@google.com, jolsa@redhat.com,
kirill@shutemov.name, mark.rutland@arm.com, mgorman@suse.de,
minchan@kernel.org, mingo@redhat.com, namhyung@kernel.org,
peterz@infradead.org, rdunlap@infradead.org, riel@surriel.com,
rientjes@google.com, rostedt@goodmis.org, sblbir@amazon.com,
shakeelb@google.com, shuah@kernel.org, sj38.park@gmail.com,
snu@amazon.de, vbabka@suse.cz, vdavydov.dev@gmail.com,
yang.shi@linux.alibaba.com, ying.huang@intel.com,
linux-damon@amazon.com, linux-mm@kvack.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC v2 7/9] mm/damon: Implement callbacks for physical memory monitoring
Date: Thu, 4 Jun 2020 18:01:28 +0200 [thread overview]
Message-ID: <b0cce3d0-07c1-0468-f64a-21cefdb74a5d@redhat.com> (raw)
In-Reply-To: <20200604155158.12760-1-sjpark@amazon.com>
On 04.06.20 17:51, SeongJae Park wrote:
> On Thu, 4 Jun 2020 17:39:49 +0200 David Hildenbrand <david@redhat.com> wrote:
>
>> On 04.06.20 17:23, SeongJae Park wrote:
>>> On Thu, 4 Jun 2020 16:58:13 +0200 David Hildenbrand <david@redhat.com> wrote:
>>>
>>>> On 04.06.20 09:26, SeongJae Park wrote:
>>>>> On Wed, 3 Jun 2020 18:09:21 +0200 David Hildenbrand <david@redhat.com> wrote:
>>>>>
>>>>>> On 03.06.20 16:11, SeongJae Park wrote:
>>>>>>> From: SeongJae Park <sjpark@amazon.de>
>>>>>>>
>>>>>>> This commit implements the four callbacks (->init_target_regions,
>>>>>>> ->update_target_regions, ->prepare_access_check, and ->check_accesses)
>>>>>>> for the basic access monitoring of the physical memory address space.
>>>>>>> By setting the callback pointers to point those, users can easily
>>>>>>> monitor the accesses to the physical memory.
>>>>>>>
>>>>>>> Internally, it uses the PTE Accessed bit, as similar to that of the
>>>>>>> virtual memory support. Also, it supports only page frames that
>>>>>>> supported by idle page tracking. Acutally, most of the code is stollen
>>>>>>> from idle page tracking. Users who want to use other access check
>>>>>>> primitives and monitor the frames that not supported with this
>>>>>>> implementation could implement their own callbacks on their own.
>>>>>>>
>>>>>>> Signed-off-by: SeongJae Park <sjpark@amazon.de>
>>>>>>> ---
>>>>>>> include/linux/damon.h | 5 ++
>>>>>>> mm/damon.c | 184 ++++++++++++++++++++++++++++++++++++++++++
>>>>>>> 2 files changed, 189 insertions(+)
>>>>>>>
>>>>>>> diff --git a/include/linux/damon.h b/include/linux/damon.h
>>>>>>> index 1a788bfd1b4e..f96503a532ea 100644
>>>>>>> --- a/include/linux/damon.h
>>>>>>> +++ b/include/linux/damon.h
>>>>>>> @@ -216,6 +216,11 @@ void kdamond_update_vm_regions(struct damon_ctx *ctx);
>>>>>>> void kdamond_prepare_vm_access_checks(struct damon_ctx *ctx);
>>>>>>> unsigned int kdamond_check_vm_accesses(struct damon_ctx *ctx);
>>>>>>>
>>>>>>> +void kdamond_init_phys_regions(struct damon_ctx *ctx);
>>>>>>> +void kdamond_update_phys_regions(struct damon_ctx *ctx);
>>>>>>> +void kdamond_prepare_phys_access_checks(struct damon_ctx *ctx);
>>>>>>> +unsigned int kdamond_check_phys_accesses(struct damon_ctx *ctx);
>>>>>>> +
>>>>>>> int damon_set_pids(struct damon_ctx *ctx, int *pids, ssize_t nr_pids);
>>>>>>> int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
>>>>>>> unsigned long aggr_int, unsigned long regions_update_int,
>>>>>>> diff --git a/mm/damon.c b/mm/damon.c
>>>>>>> index f5cbc97a3bbc..6a5c6d540580 100644
>>>>>>> --- a/mm/damon.c
>>>>>>> +++ b/mm/damon.c
>>>>>>> @@ -19,7 +19,9 @@
>>>>>>> #include <linux/mm.h>
>>>>>>> #include <linux/module.h>
>>>>>>> #include <linux/page_idle.h>
>>>>>>> +#include <linux/pagemap.h>
>>>>>>> #include <linux/random.h>
>>>>>>> +#include <linux/rmap.h>
>>>>>>> #include <linux/sched/mm.h>
>>>>>>> #include <linux/sched/task.h>
>>>>>>> #include <linux/slab.h>
>>>>>>> @@ -480,6 +482,11 @@ void kdamond_init_vm_regions(struct damon_ctx *ctx)
>>>>>>> }
>>>>>>> }
>>>>>>>
>>>>>>> +/* Do nothing. Users should set the initial regions by themselves */
>>>>>>> +void kdamond_init_phys_regions(struct damon_ctx *ctx)
>>>>>>> +{
>>>>>>> +}
>>>>>>> +
>>>>>>> static void damon_mkold(struct mm_struct *mm, unsigned long addr)
>>>>>>> {
>>>>>>> pte_t *pte = NULL;
>>>>>>> @@ -611,6 +618,178 @@ unsigned int kdamond_check_vm_accesses(struct damon_ctx *ctx)
>>>>>>> return max_nr_accesses;
>>>>>>> }
>>>>>>>
>>>>>>> +/* access check functions for physical address based regions */
>>>>>>> +
>>>>>>> +/* This code is stollen from page_idle.c */
>>>>>>> +static struct page *damon_phys_get_page(unsigned long pfn)
>>>>>>> +{
>>>>>>> + struct page *page;
>>>>>>> + pg_data_t *pgdat;
>>>>>>> +
>>>>>>> + if (!pfn_valid(pfn))
>>>>>>> + return NULL;
>>>>>>> +
>>>>>>
>>>>>> Who provides these pfns? Can these be random pfns, supplied unchecked by
>>>>>> user space? Or are they at least mapped into some user space process?
>>>>>
>>>>> Your guess is right, users can give random physical address and that will be
>>>>> translated into pfn.
>>>>>
>>>>
>>>> Note the difference to idle tracking: "Idle page tracking only considers
>>>> user memory pages", this is very different to your use case. Note that
>>>> this is why there is no pfn_to_online_page() check in page idle code.
>>>
>>> My use case is same to that of idle page. I also ignore non-user pages.
>>> Actually, this function is for filtering of the non-user pages, which is simply
>>> stollen from the page_idle.
>>
>> Okay, that is valuable information, I missed that. The comment in
>> page_idle.c is actually pretty valuable.
>>
>> In both cases, user space can provide random physical address but you
>> will only care about user pages. Understood.
>>
>> That turns things less dangerous. :)
>
> Glad to hear this. I will refine this point in the next spin! :)
Perfect, when I read "physical address space", I was assuming you would
magically track access to e.g., memmap, page tables and stuff like that.
And I wondered how you would do that :D
BTW now that I realized that as we only care about LRU pages,
page_to_online_page() is sufficient, no need to worry about dax/pmem.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-06-04 16:02 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-03 14:11 [RFC v2 0/9] DAMON: Support Access Monitoring of Any Address Space Including Physical Memory SeongJae Park
2020-06-03 14:11 ` [RFC v2 1/9] mm/damon: Use vm-independent address range concept SeongJae Park
2020-06-03 14:11 ` [RFC v2 2/9] mm/damon: Clean up code using 'struct damon_addr_range' SeongJae Park
2020-06-03 14:11 ` [RFC v2 3/9] mm/damon: Make monitoring target regions init/update configurable SeongJae Park
2020-06-03 14:11 ` [RFC v2 4/9] mm/damon/debugfs: Allow users to set initial monitoring target regions SeongJae Park
2020-06-03 14:11 ` [RFC v2 5/9] Docs/damon: Document 'initial_regions' feature SeongJae Park
2020-06-03 14:11 ` [RFC v2 6/9] mm/damon: Make access check primitive configurable SeongJae Park
2020-06-03 14:11 ` [RFC v2 7/9] mm/damon: Implement callbacks for physical memory monitoring SeongJae Park
2020-06-03 16:09 ` David Hildenbrand
2020-06-04 7:26 ` SeongJae Park
2020-06-04 14:58 ` David Hildenbrand
2020-06-04 15:23 ` SeongJae Park
2020-06-04 15:39 ` David Hildenbrand
2020-06-04 15:51 ` SeongJae Park
2020-06-04 16:01 ` David Hildenbrand [this message]
2020-06-03 14:11 ` [RFC v2 8/9] mm/damon/debugfs: Support " SeongJae Park
2020-06-03 14:11 ` [RFC v2 9/9] Docs/damon: Document physical memory monitoring support SeongJae Park
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