mainlining shenanigans
5b24eeef06
Patch series "mm, device-dax: Introduce compound pages in devmap", v7.
This series converts device-dax to use compound pages, and moves away
from the 'struct page per basepage on PMD/PUD' that is done today.
Doing so
1) unlocks a few noticeable improvements on unpin_user_pages() and
makes device-dax+altmap case 4x times faster in pinning (numbers
below and in last patch)
2) as mentioned in various other threads it's one important step
towards cleaning up ZONE_DEVICE refcounting.
I've split the compound pages on devmap part from the rest based on
recent discussions on devmap pending and future work planned[5][6].
There is consensus that device-dax should be using compound pages to
represent its PMD/PUDs just like HugeTLB and THP, and that leads to less
specialization of the dax parts. I will pursue the rest of the work in
parallel once this part is merged, particular the GUP-{slow,fast}
improvements [7] and the tail struct page deduplication memory savings
part[8].
To summarize what the series does:
Patch 1: Prepare hwpoisoning to work with dax compound pages.
Patches 2-3: Split the current utility function of prep_compound_page()
into head and tail and use those two helpers where appropriate to take
advantage of caches being warm after __init_single_page(). This is used
when initializing zone device when we bring up device-dax namespaces.
Patches 4-10: Add devmap support for compound pages in device-dax.
memmap_init_zone_device() initialize its metadata as compound pages, and
it introduces a new devmap property known as vmemmap_shift which
outlines how the vmemmap is structured (defaults to base pages as done
today). The property describe the page order of the metadata
essentially. While at it do a few cleanups in device-dax in patches
5-9. Finally enable device-dax usage of devmap @vmemmap_shift to a
value based on its own @align property. @vmemmap_shift returns 0 by
default (which is today's case of base pages in devmap, like fsdax or
the others) and the usage of compound devmap is optional. Starting with
device-dax (*not* fsdax) we enable it by default. There are a few
pinning improvements particular on the unpinning case and altmap, as
well as unpin_user_page_range_dirty_lock() being just as effective as
THP/hugetlb[0] pages.
$ gup_test -f /dev/dax1.0 -m 16384 -r 10 -S -a -n 512 -w
(pin_user_pages_fast 2M pages) put:~71 ms -> put:~22 ms
[altmap]
(pin_user_pages_fast 2M pages) get:~524ms put:~525 ms -> get: ~127ms put:~71ms
$ gup_test -f /dev/dax1.0 -m 129022 -r 10 -S -a -n 512 -w
(pin_user_pages_fast 2M pages) put:~513 ms -> put:~188 ms
[altmap with -m 127004]
(pin_user_pages_fast 2M pages) get:~4.1 secs put:~4.12 secs -> get:~1sec put:~563ms
Tested on x86 with 1Tb+ of pmem (alongside registering it with RDMA with
and without altmap), alongside gup_test selftests with dynamic dax
regions and static dax regions. Coupled with ndctl unit tests for
dynamic dax devices that exercise all of this. Note, for dynamic dax
regions I had to revert commit
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.