From: Ralph Campbell <rcampbell@nvidia.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: <linux-mm@kvack.org>, <kvm-ppc@vger.kernel.org>,
<nouveau@lists.freedesktop.org>, <linux-kernel@vger.kernel.org>,
Dan Williams <dan.j.williams@intel.com>,
Ira Weiny <ira.weiny@intel.com>,
Jerome Glisse <jglisse@redhat.com>,
John Hubbard <jhubbard@nvidia.com>,
Alistair Popple <apopple@nvidia.com>,
Christoph Hellwig <hch@lst.de>, Jason Gunthorpe <jgg@nvidia.com>,
Bharata B Rao <bharata@linux.ibm.com>, Zi Yan <ziy@nvidia.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Yang Shi <yang.shi@linux.alibaba.com>,
Paul Mackerras <paulus@ozlabs.org>,
Ben Skeggs <bskeggs@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH v3 0/2] mm: remove extra ZONE_DEVICE struct page refcount
Date: Thu, 13 May 2021 10:35:39 -0700 [thread overview]
Message-ID: <750b6107-71c5-d17f-60b5-b4e8edb3aa99@nvidia.com> (raw)
In-Reply-To: <YJ0mVAK7OjwIGnMe@casper.infradead.org>
On 5/13/21 6:15 AM, Matthew Wilcox wrote:
> On Thu, Oct 01, 2020 at 11:17:13AM -0700, Ralph Campbell wrote:
>> This is still an RFC because after looking at the pmem/dax code some
>> more, I realized that the ZONE_DEVICE struct pages are being inserted
>> into the process' page tables with vmf_insert_mixed() and a zero
>> refcount on the ZONE_DEVICE struct page. This is sort of OK because
>> insert_pfn() increments the reference count on the pgmap which is what
>> prevents memunmap_pages() from freeing the struct pages and it doesn't
>> check for a non-zero struct page reference count.
>> But, any calls to get_page() will hit the VM_BUG_ON_PAGE() that
>> checks for a reference count == 0.
>
> This seems to have gone quiet. What needs to happen to resurrect this?
>
The main thing I need is time. I have been tied up with other commitments,
there has been a lot of changes going on in FS/DAX and the page cache,
and FS/DAX doesn't use the page reference count to indicate the page is
"free" but rather that it is "idle" so I need a lot of time to really
understand why FS/DAX isn't just any FS on top of a DAX block device.
I too wish this was easier to fix.
WARNING: multiple messages have this Message-ID (diff)
From: Ralph Campbell <rcampbell@nvidia.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>, Zi Yan <ziy@nvidia.com>,
nouveau@lists.freedesktop.org,
Alistair Popple <apopple@nvidia.com>,
linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org,
Bharata B Rao <bharata@linux.ibm.com>,
Paul Mackerras <paulus@ozlabs.org>,
linux-mm@kvack.org, Ben Skeggs <bskeggs@redhat.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Dan Williams <dan.j.williams@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ira Weiny <ira.weiny@intel.com>, Christoph Hellwig <hch@lst.de>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [Nouveau] [RFC PATCH v3 0/2] mm: remove extra ZONE_DEVICE struct page refcount
Date: Thu, 13 May 2021 10:35:39 -0700 [thread overview]
Message-ID: <750b6107-71c5-d17f-60b5-b4e8edb3aa99@nvidia.com> (raw)
In-Reply-To: <YJ0mVAK7OjwIGnMe@casper.infradead.org>
On 5/13/21 6:15 AM, Matthew Wilcox wrote:
> On Thu, Oct 01, 2020 at 11:17:13AM -0700, Ralph Campbell wrote:
>> This is still an RFC because after looking at the pmem/dax code some
>> more, I realized that the ZONE_DEVICE struct pages are being inserted
>> into the process' page tables with vmf_insert_mixed() and a zero
>> refcount on the ZONE_DEVICE struct page. This is sort of OK because
>> insert_pfn() increments the reference count on the pgmap which is what
>> prevents memunmap_pages() from freeing the struct pages and it doesn't
>> check for a non-zero struct page reference count.
>> But, any calls to get_page() will hit the VM_BUG_ON_PAGE() that
>> checks for a reference count == 0.
>
> This seems to have gone quiet. What needs to happen to resurrect this?
>
The main thing I need is time. I have been tied up with other commitments,
there has been a lot of changes going on in FS/DAX and the page cache,
and FS/DAX doesn't use the page reference count to indicate the page is
"free" but rather that it is "idle" so I need a lot of time to really
understand why FS/DAX isn't just any FS on top of a DAX block device.
I too wish this was easier to fix.
_______________________________________________
Nouveau mailing list
Nouveau@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/nouveau
WARNING: multiple messages have this Message-ID (diff)
From: Ralph Campbell <rcampbell@nvidia.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-mm@kvack.org, kvm-ppc@vger.kernel.org,
nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org,
Dan Williams <dan.j.williams@intel.com>,
Ira Weiny <ira.weiny@intel.com>,
Jerome Glisse <jglisse@redhat.com>,
John Hubbard <jhubbard@nvidia.com>,
Alistair Popple <apopple@nvidia.com>,
Christoph Hellwig <hch@lst.de>, Jason Gunthorpe <jgg@nvidia.com>,
Bharata B Rao <bharata@linux.ibm.com>, Zi Yan <ziy@nvidia.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Yang Shi <yang.shi@linux.alibaba.com>,
Paul Mackerras <paulus@ozlabs.org>,
Ben Skeggs <bskeggs@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH v3 0/2] mm: remove extra ZONE_DEVICE struct page refcount
Date: Thu, 13 May 2021 17:35:39 +0000 [thread overview]
Message-ID: <750b6107-71c5-d17f-60b5-b4e8edb3aa99@nvidia.com> (raw)
In-Reply-To: <YJ0mVAK7OjwIGnMe@casper.infradead.org>
On 5/13/21 6:15 AM, Matthew Wilcox wrote:
> On Thu, Oct 01, 2020 at 11:17:13AM -0700, Ralph Campbell wrote:
>> This is still an RFC because after looking at the pmem/dax code some
>> more, I realized that the ZONE_DEVICE struct pages are being inserted
>> into the process' page tables with vmf_insert_mixed() and a zero
>> refcount on the ZONE_DEVICE struct page. This is sort of OK because
>> insert_pfn() increments the reference count on the pgmap which is what
>> prevents memunmap_pages() from freeing the struct pages and it doesn't
>> check for a non-zero struct page reference count.
>> But, any calls to get_page() will hit the VM_BUG_ON_PAGE() that
>> checks for a reference count = 0.
>
> This seems to have gone quiet. What needs to happen to resurrect this?
>
The main thing I need is time. I have been tied up with other commitments,
there has been a lot of changes going on in FS/DAX and the page cache,
and FS/DAX doesn't use the page reference count to indicate the page is
"free" but rather that it is "idle" so I need a lot of time to really
understand why FS/DAX isn't just any FS on top of a DAX block device.
I too wish this was easier to fix.
next prev parent reply other threads:[~2021-05-13 17:36 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 18:17 [RFC PATCH v3 0/2] mm: remove extra ZONE_DEVICE struct page refcount Ralph Campbell
2020-10-01 18:17 ` Ralph Campbell
2020-10-01 18:17 ` Ralph Campbell
2020-10-01 18:17 ` [RFC PATCH v3 1/2] ext4/xfs: add page refcount helper Ralph Campbell
2020-10-01 18:17 ` Ralph Campbell
2020-10-01 18:17 ` Ralph Campbell
2020-10-02 5:56 ` Christoph Hellwig
2020-10-02 5:56 ` Christoph Hellwig
2020-10-05 16:29 ` Ralph Campbell
2020-10-05 16:29 ` Ralph Campbell
2020-10-05 16:29 ` Ralph Campbell
2020-10-01 18:17 ` [RFC PATCH v3 2/2] mm: remove extra ZONE_DEVICE struct page refcount Ralph Campbell
2020-10-01 18:17 ` Ralph Campbell
2020-10-01 18:17 ` Ralph Campbell
2020-10-02 5:59 ` Christoph Hellwig
2020-10-02 5:59 ` Christoph Hellwig
2020-10-05 16:40 ` Ralph Campbell
2020-10-05 16:40 ` Ralph Campbell
2020-10-05 16:40 ` Ralph Campbell
2020-10-08 5:17 ` Ram Pai
2020-10-08 5:17 ` Ram Pai
2020-10-08 16:45 ` Ralph Campbell
2020-10-08 16:45 ` Ralph Campbell
2020-10-08 16:45 ` Ralph Campbell
2020-10-05 16:56 ` [RFC PATCH v3 0/2] " Matthew Wilcox
2020-10-05 16:56 ` Matthew Wilcox
2020-10-05 18:24 ` Dan Williams
2020-10-05 18:24 ` Dan Williams
2020-10-05 18:24 ` Dan Williams
2021-05-13 13:15 ` Matthew Wilcox
2021-05-13 13:15 ` Matthew Wilcox
2021-05-13 13:15 ` [Nouveau] " Matthew Wilcox
2021-05-13 17:35 ` Ralph Campbell [this message]
2021-05-13 17:35 ` Ralph Campbell
2021-05-13 17:35 ` [Nouveau] " Ralph Campbell
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