From: Peter Xu <peterx@redhat.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: "Andrei Vagin" <avagin@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Muhammad Usama Anjum" <usama.anjum@collabora.com>,
"David Hildenbrand" <david@redhat.com>,
"Michał Mirosław" <emmir@google.com>,
"Danylo Mocherniuk" <mdanylo@google.com>,
"Paul Gofman" <pgofman@codeweavers.com>,
"Cyrill Gorcunov" <gorcunov@gmail.com>,
"Nadav Amit" <namit@vmware.com>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Shuah Khan" <shuah@kernel.org>,
"Christian Brauner" <brauner@kernel.org>,
"Yang Shi" <shy828301@gmail.com>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Liam R . Howlett" <Liam.Howlett@oracle.com>,
"Yun Zhou" <yun.zhou@windriver.com>,
"Suren Baghdasaryan" <surenb@google.com>,
"Alex Sierra" <alex.sierra@amd.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Pasha Tatashin" <pasha.tatashin@soleen.com>,
"Axel Rasmussen" <axelrasmussen@google.com>,
"Gustavo A . R . Silva" <gustavoars@kernel.org>,
"Dan Williams" <dan.j.williams@intel.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
"Greg KH" <gregkh@linuxfoundation.org>,
kernel@collabora.com
Subject: Re: [PATCH v11 0/7] Implement IOCTL to get and optionally clear info about PTEs
Date: Tue, 21 Mar 2023 11:10:02 -0400 [thread overview]
Message-ID: <ZBnIyjTJ5yfxpcgs@x1n> (raw)
In-Reply-To: <ZBmmEfgq8QBAKPFN@kernel.org>
On Tue, Mar 21, 2023 at 02:41:53PM +0200, Mike Rapoport wrote:
> On Mon, Mar 20, 2023 at 11:30:00AM -0700, Andrei Vagin wrote:
> > On Thu, Mar 9, 2023 at 11:58 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> > >
> > > On Thu, 9 Mar 2023 18:57:11 +0500 Muhammad Usama Anjum <usama.anjum@collabora.com> wrote:
> > >
> > > > The information related to pages if the page is file mapped, present and
> > > > swapped is required for the CRIU project [5][6]. The addition of the
> > > > required mask, any mask, excluded mask and return masks are also required
> > > > for the CRIU project [5].
> > >
> > > It's a ton of new code and what I'm not seeing in here (might have
> > > missed it?) is a clear statement of the value of this feature to our
> > > users.
> > >
> > > I see hints that CRIU would like it, but no description of how valuable
> > > this is to CRIU's users.
> >
> > Hi Andrew,
> >
> > The current interface works for CRIU, and I can't say we have anything
> > critical with it right now.
> >
> > On the other hand, the new interface has a number of significant improvements:
> >
> > * it is more granular and allows us to track changed pages more
> > effectively. The current interface can clear dirty bits for the entire
> > process only. In addition, reading info about pages is a separate
> > operation. It means we must freeze the process to read information
> > about all its pages, reset dirty bits, only then we can start dumping
> > pages. The information about pages becomes more and more outdated,
> > while we are processing pages. The new interface solves both these
> > downsides. First, it allows us to read pte bits and clear the
> > soft-dirty bit atomically. It means that CRIU will not need to freeze
> > processes to pre-dump their memory. Second, it clears soft-dirty bits
> > for a specified region of memory. It means CRIU will have actual info
> > about pages to the moment of dumping them.
> >
> > * The new interface has to be much faster because basic page filtering
> > is happening in the kernel. With the old interface, we have to read
> > pagemap for each page.
>
> There is still a caveat in using userfaultfd for tracking dirty pages in
> CRIU because we still don't support C/R of processes that use uffd.
This reminded me whether the interface can also expose soft-dirty as a
ranged soft-dirty collector too to replace existing pagemap read()s? Just
in case userfault cannot be used. The code addition should be trivial IIUC.
Then maybe PAGE_IS_WRITTEN will be a name too generic, it can be two bits
PAGE_IS_UFFD_WP and PAGE_IS_SOFT_DIRTY, having PAGE_IS_UFFD_WP the inverted
meaning of current PAGE_IS_WRITTEN.
--
Peter Xu
prev parent reply other threads:[~2023-03-21 15:11 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-09 13:57 [PATCH v11 0/7] Implement IOCTL to get and optionally clear info about PTEs Muhammad Usama Anjum
2023-03-09 13:57 ` [PATCH v11 1/7] userfaultfd: Add UFFD WP Async support Muhammad Usama Anjum
2023-03-16 19:20 ` Peter Xu
2023-03-17 14:00 ` Muhammad Usama Anjum
2023-03-21 12:21 ` Muhammad Usama Anjum
2023-03-21 19:25 ` Peter Xu
2023-03-23 15:43 ` Muhammad Usama Anjum
2023-03-09 13:57 ` [PATCH v11 2/7] userfaultfd: Define dummy uffd_wp_range() Muhammad Usama Anjum
2023-03-16 7:02 ` Mike Rapoport
2023-03-16 18:05 ` Muhammad Usama Anjum
2023-03-09 13:57 ` [PATCH v11 3/7] userfaultfd: update documentation to describe UFFD_FEATURE_WP_ASYNC Muhammad Usama Anjum
2023-03-09 13:57 ` [PATCH v11 4/7] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs Muhammad Usama Anjum
2023-03-13 16:02 ` Michał Mirosław
2023-03-16 17:53 ` Muhammad Usama Anjum
2023-03-16 21:28 ` Michał Mirosław
2023-03-17 12:43 ` Muhammad Usama Anjum
2023-03-17 14:15 ` Michał Mirosław
2023-03-20 6:08 ` Muhammad Usama Anjum
2023-03-15 15:55 ` Peter Xu
2023-03-15 16:54 ` Muhammad Usama Anjum
2023-03-15 19:53 ` Peter Xu
2023-03-16 5:17 ` Muhammad Usama Anjum
2023-03-09 13:57 ` [PATCH v11 5/7] tools headers UAPI: Update linux/fs.h with the kernel sources Muhammad Usama Anjum
2023-03-09 13:57 ` [PATCH v11 6/7] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL Muhammad Usama Anjum
2023-03-09 13:57 ` [PATCH v11 7/7] selftests: mm: add pagemap ioctl tests Muhammad Usama Anjum
2023-03-09 19:58 ` [PATCH v11 0/7] Implement IOCTL to get and optionally clear info about PTEs Andrew Morton
2023-03-09 22:24 ` Muhammad Usama Anjum
2023-03-20 18:30 ` Andrei Vagin
2023-03-21 12:41 ` Mike Rapoport
2023-03-21 15:10 ` Peter Xu [this message]
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