From: John Hubbard <jhubbard@nvidia.com>
To: Vlastimil Babka <vbabka@suse.cz>, Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Christoph Hellwig <hch@infradead.org>,
Ira Weiny <ira.weiny@intel.com>, Jan Kara <jack@suse.cz>,
Jason Gunthorpe <jgg@ziepe.ca>,
Jerome Glisse <jglisse@redhat.com>,
LKML <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
<linux-fsdevel@vger.kernel.org>,
Dan Williams <dan.j.williams@intel.com>,
Daniel Black <daniel@linux.ibm.com>,
Matthew Wilcox <willy@infradead.org>,
Mike Kravetz <mike.kravetz@oracle.com>
Subject: Re: [PATCH 1/3] mm/mlock.c: convert put_page() to put_user_page*()
Date: Thu, 8 Aug 2019 15:59:15 -0700 [thread overview]
Message-ID: <d1ecb0d4-ea6a-637d-7029-687b950b783f@nvidia.com> (raw)
In-Reply-To: <306128f9-8cc6-761b-9b05-578edf6cce56@nvidia.com>
On 8/8/19 12:20 PM, John Hubbard wrote:
> On 8/8/19 4:09 AM, Vlastimil Babka wrote:
>> On 8/8/19 8:21 AM, Michal Hocko wrote:
>>> On Wed 07-08-19 16:32:08, John Hubbard wrote:
>>>> On 8/7/19 4:01 AM, Michal Hocko wrote:
>>>>> On Mon 05-08-19 15:20:17, john.hubbard@gmail.com wrote:
>>>>>> From: John Hubbard <jhubbard@nvidia.com>
>>>> Actually, I think follow_page_mask() gets all the pages, right? And the
>>>> get_page() in __munlock_pagevec_fill() is there to allow a pagevec_release()
>>>> later.
>>>
>>> Maybe I am misreading the code (looking at Linus tree) but munlock_vma_pages_range
>>> calls follow_page for the start address and then if not THP tries to
>>> fill up the pagevec with few more pages (up to end), do the shortcut
>>> via manual pte walk as an optimization and use generic get_page there.
>>
>
> Yes, I see it finally, thanks. :)
>
>> That's true. However, I'm not sure munlocking is where the
>> put_user_page() machinery is intended to be used anyway? These are
>> short-term pins for struct page manipulation, not e.g. dirtying of page
>> contents. Reading commit fc1d8e7cca2d I don't think this case falls
>> within the reasoning there. Perhaps not all GUP users should be
>> converted to the planned separate GUP tracking, and instead we should
>> have a GUP/follow_page_mask() variant that keeps using get_page/put_page?
>>
>
> Interesting. So far, the approach has been to get all the gup callers to
> release via put_user_page(), but if we add in Jan's and Ira's vaddr_pin_pages()
> wrapper, then maybe we could leave some sites unconverted.
>
> However, in order to do so, we would have to change things so that we have
> one set of APIs (gup) that do *not* increment a pin count, and another set
> (vaddr_pin_pages) that do.
>
> Is that where we want to go...?
>
Oh, and meanwhile, I'm leaning toward a cheap fix: just use gup_fast() instead
of get_page(), and also fix the releasing code. So this incremental patch, on
top of the existing one, should do it:
diff --git a/mm/mlock.c b/mm/mlock.c
index b980e6270e8a..2ea272c6fee3 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -318,18 +318,14 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
/*
* We won't be munlocking this page in the next phase
* but we still need to release the follow_page_mask()
- * pin. We cannot do it under lru_lock however. If it's
- * the last pin, __page_cache_release() would deadlock.
+ * pin.
*/
- pagevec_add(&pvec_putback, pvec->pages[i]);
+ put_user_page(pages[i]);
pvec->pages[i] = NULL;
}
__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
spin_unlock_irq(&zone->zone_pgdat->lru_lock);
- /* Now we can release pins of pages that we are not munlocking */
- pagevec_release(&pvec_putback);
-
/* Phase 2: page munlock */
for (i = 0; i < nr; i++) {
struct page *page = pvec->pages[i];
@@ -394,6 +390,8 @@ static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,
start += PAGE_SIZE;
while (start < end) {
struct page *page = NULL;
+ int ret;
+
pte++;
if (pte_present(*pte))
page = vm_normal_page(vma, start, *pte);
@@ -411,7 +409,13 @@ static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,
if (PageTransCompound(page))
break;
- get_page(page);
+ /*
+ * Use get_user_pages_fast(), instead of get_page() so that the
+ * releasing code can unconditionally call put_user_page().
+ */
+ ret = get_user_pages_fast(start, 1, 0, &page);
+ if (ret != 1)
+ break;
/*
* Increase the address that will be returned *before* the
* eventual break due to pvec becoming full by adding the page
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2019-08-08 22:59 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-05 22:20 [PATCH 0/3] mm/: 3 more put_user_page() conversions john.hubbard
2019-08-05 22:20 ` [PATCH 1/3] mm/mlock.c: convert put_page() to put_user_page*() john.hubbard
2019-08-07 11:01 ` Michal Hocko
2019-08-07 23:32 ` John Hubbard
2019-08-08 6:21 ` Michal Hocko
2019-08-08 11:09 ` Vlastimil Babka
2019-08-08 19:20 ` John Hubbard
2019-08-08 22:59 ` John Hubbard [this message]
2019-08-08 23:41 ` Ira Weiny
2019-08-08 23:57 ` John Hubbard
2019-08-09 18:22 ` Weiny, Ira
2019-08-09 8:12 ` Vlastimil Babka
2019-08-09 8:23 ` Michal Hocko
2019-08-09 9:05 ` John Hubbard
2019-08-09 9:16 ` Michal Hocko
2019-08-09 13:58 ` Jan Kara
2019-08-09 17:52 ` Michal Hocko
2019-08-09 18:14 ` Weiny, Ira
2019-08-09 18:36 ` John Hubbard
2019-08-05 22:20 ` [PATCH 2/3] mm/mempolicy.c: " john.hubbard
2019-08-05 22:20 ` [PATCH 3/3] mm/ksm: " john.hubbard
2019-08-06 21:59 ` [PATCH 0/3] mm/: 3 more put_user_page() conversions Andrew Morton
2019-08-06 22:05 ` John Hubbard
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