[v7,00/11] mm, device-dax: Introduce compound pages in devmap

Message

Joao Martins Dec. 2, 2021, 8:44 p.m. UTC

Changes since v6[10]:

* Patch 4, Wrap commit message to 73 characters max (Christoph Hellwig)
* Patch 4, Move pfn_next() in for_each_device_pfn() to new line (Christoph Hellwig)
* Patch 4, Move pfn range computation to a pfn_len() helper. (Christoph Hellwig) 
* Patch 9, Remove @fault_size as it's no longer used (also reported by kbuild robot).
* New Patch 10, remove unneeded @pfn output parameter from dev_dax_huge_fault()
(Christoph Helwig) -- this is done in a new patch
"device-dax: remove pfn from __dev_dax_{pte,pmd,pud}_fault()"

Series is meant to replace what's merged in mmotm/linux-next. Only patch 4 has
changed  but I added a new cleanup patch suggested by Christoph which is what
prompted to send the entire series.  This was based on linux-next tag
next-20211124 (commit 4b74e088fef6) same as to be replaced v6. 

Let me know if there's another preferred way of doing this (e.g. send patch 10
separate as a follow up and just picking up this series patch 4 as mmotm
already has patch 9 fix)).

---

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 8aa83e6395 ("x86/setup: Call early_reserve_memory() earlier"), it
is a known issue that this commit broke efi_fake_mem=.

Patches apply on top of linux-next tag next-20211124 (commit 4b74e088fef6).

Thanks for all the review so far.

As always, Comments and suggestions very much appreciated!

Older Changelog,

v5[9] -> v6[10]:

* Keep @dev on the previous line to improve readability on 
patch 5 (Christoph Hellwig)
* Document is_static() function to clarify what are static and
dynamic dax regions in patch 7 (Christoph Hellwig)
* Deduce @f_mapping and @pgmap from vmf->vma->vm_file to reduce
the number of arguments of set_{page,compound}_mapping() in last
patch (Christoph Hellwig)
* Factor out @mapping initialization to a separate helper ([new] patch 8)
and rename set_page_mapping() to dax_set_mapping() in the process.
* Remove set_compound_mapping() and instead adjust dax_set_mapping()
to handle @vmemmap_shift case on the last patch. This greatly
simplifies the last patch, and addresses a similar comment by Christoph
on having an earlier return. No functional change on the changes
to dax_set_mapping compared to its earlier version so I retained
Dan's Rb on last patch.
* Initialize the mapping prior to inserting the PTE/PMD/PUD as opposed
to after the fact. ([new] patch 9, Jason Gunthorpe)

Patches 8 and 9 are new (small cleanups) in v6.
Patches 6 - 9 are the ones missing Rb tags.

v4[4] -> v5[9]:

* Remove patches 8-14 as they will go in 2 separate (parallel) series;
* Rename @geometry to @vmemmap_shift (Christoph Hellwig)
* Make @vmemmap_shift an order rather than nr of pages (Christoph Hellwig)
* Consequently remove helper pgmap_geometry_order() as it's no longer
needed, in place of accessing directly the structure member [Patch 4 and 8]
* Rename pgmap_geometry() to pgmap_vmemmap_nr() in patches 4 and 8;
* Remove usage of pgmap_geometry() in favour for testing
  @vmemmap_shift for non-zero directly directly in patch 8;
* Patch 5 is new for using `struct_size()` (Dan Williams)
* Add a 'static_dev_dax()' helper for testing pgmap == NULL handling
for dynamic dax devices.
* Expand patch 6 to be explicitly on those !pgmap cases, and replace
those with static_dev_dax().
* Add performance numbers on patch 8 on gup/pin_user_pages() numbers with
this series.
* Massage commit description to remove mentions of @geometry.
* Add Dan's Reviewed-by on patch 8 (Dan Williams)

v3[3] -> v4[4]:

 * Collect Dan's Reviewed-by on patches 1-5,8,9,11
 * Collect Muchun Reviewed-by on patch 1,2,11
 * Reorder patches to first introduce compound pages in ZONE_DEVICE with
 device-dax (for pmem) as first user (patches 1-8) followed by implementing
 the sparse-vmemmap changes for minimize struct page overhead for devmap (patches 9-14)
 * Eliminate remnant @align references to use @geometry (Dan)
 * Convert mentions of 'compound pagemap' to 'compound devmap' throughout
   the series to avoid confusions of this work conflicting/referring to
   anything Folio or pagemap related.
 * Delete pgmap_pfn_geometry() on patch 4
   and rework other patches to use pgmap_geometry() instead (Dan)
 * Convert @geometry to be a number of pages rather than page size in patch 4 (Dan)
 * Make pgmap_geometry() more readable (Christoph)
 * Simplify pgmap refcount pfn computation in memremap_pages() (Christoph)
 * Rework memmap_init_compound() in patch 4 to use the same style as
 memmap_init_zone_device i.e. iterating over PFNs, rather than struct pages (Dan)
 * Add comment on devmap prep_compound_head callsite explaining why it needs
 to be used after first+second tail pages have been initialized (Dan, Jane)
 * Initialize tail page refcount to zero in patch 4
 * Make sure pfn_next() iterate over compound pages (rather than base page) in
 patch 4 to tackle the zone_device elevated page refcount.
 [ Note these last two bullet points above are unneeded once this patch is merged:
   https://lore.kernel.org/linux-mm/[e-mail]/ ]
 * Remove usage of ternary operator when computing @end in gup_device_huge() in patch 8 (Dan)
 * Remove pinned_head variable in patch 8
 * Remove put_dev_pagemap() need for compound case as that is now fixed for the general case
 in patch 8
 * Switch to PageHead() instead of PageCompound() as we only work with either base pages
 or head pages in patch 8 (Matthew)
 * Fix kdoc of @altmap and improve kdoc for @pgmap in patch 9 (Dan)
 * Fix up missing return in vmemmap_populate_address() in patch 10
 * Change error handling style in all patches (Dan)
 * Change title of vmemmap_dedup.rst to be more representative of the purpose in patch 12 (Dan)
 * Move some of the section and subsection tail page reuse code into helpers
 reuse_compound_section() and compound_section_tail_page() for readability in patch 12 (Dan)
 * Commit description fixes for clearity in various patches (Dan)
 * Add pgmap_geometry_order() helper and
   drop unneeded geometry_size, order variables in patch 12
 * Drop unneeded byte based computation to be PFN in patch 12
 * Handle the dynamic dax region properly when ensuring a stable dev_dax->pgmap in patch 6.
 * Add a compound_nr_pages() helper and use it in memmap_init_zone_device to calculate
 the number of unique struct pages to initialize depending on @altmap existence in patch 13 (Dan)
 * Add compound_section_tail_huge_page() for the tail page PMD reuse in patch 14 (Dan)
 * Reword cover letter.

v2 -> v3[3]:
 * Collect Mike's Ack on patch 2 (Mike)
 * Collect Naoya's Reviewed-by on patch 1 (Naoya)
 * Rename compound_pagemaps.rst doc page (and its mentions) to vmemmap_dedup.rst (Mike, Muchun)
 * Rebased to next-20210714

v1[1] -> v2[2]:

 (New patches 7, 10, 11)
 * Remove occurences of 'we' in the commit descriptions (now for real) [Dan]
 * Add comment on top of compound_head() for fsdax (Patch 1) [Dan]
 * Massage commit descriptions of cleanup/refactor patches to reflect [Dan]
 that it's in preparation for bigger infra in sparse-vmemmap. (Patch 2,3,5) [Dan]
 * Greatly improve all commit messages in terms of grammar/wording and clearity. [Dan]
 * Rename variable/helpers from dev_pagemap::align to @geometry, reflecting
 tht it's not the same thing as dev_dax->align, Patch 4 [Dan]
 * Move compound page init logic into separate memmap_init_compound() helper, Patch 4 [Dan]
 * Simplify patch 9 as a result of having compound initialization differently [Dan]
 * Rename @pfn_align variable in memmap_init_zone_device to @pfns_per_compound [Dan]
 * Rename Subject of patch 6 [Dan]
 * Move hugetlb_vmemmap.c comment block to Documentation/vm Patch 7 [Dan]
 * Add some type-safety to @block and use 'struct page *' rather than
 void, Patch 8 [Dan]
 * Add some comments to less obvious parts on 1G compound page case, Patch 8 [Dan]
 * Remove vmemmap lookup function in place of
 pmd_off_k() + pte_offset_kernel() given some guarantees on section onlining
 serialization, Patch 8
 * Add a comment to get_page() mentioning where/how it is, Patch 8 freed [Dan]
 * Add docs about device-dax usage of tail dedup technique in newly added
 compound_pagemaps.rst doc entry.
 * Add cleanup patch for device-dax for ensuring dev_dax::pgmap is always set [Dan]
 * Add cleanup patch for device-dax for using ALIGN() [Dan]
 * Store pinned head in separate @pinned_head variable and fix error case, patch 13 [Dan]
 * Add comment on difference of @next value for PageCompound(), patch 13 [Dan]
 * Move PUD compound page to be last patch [Dan]
 * Add vmemmap layout for PUD compound geometry in compound_pagemaps.rst doc, patch 14 [Dan]
 * Rebased to next-20210617 

 RFC[0] -> v1:
 (New patches 1-3, 5-8 but the diffstat isn't that different)
 * Fix hwpoisoning of devmap pages reported by Jane (Patch 1 is new in v1)
 * Fix/Massage commit messages to be more clear and remove the 'we' occurences (Dan, John, Matthew)
 * Use pfn_align to be clear it's nr of pages for @align value (John, Dan)
 * Add two helpers pgmap_align() and pgmap_pfn_align() as accessors of pgmap->align;
 * Remove the gup_device_compound_huge special path and have the same code
   work both ways while special casing when devmap page is compound (Jason, John)
 * Avoid usage of vmemmap_populate_basepages() and introduce a first class
   loop that doesn't care about passing an altmap for memmap reuse. (Dan)
 * Completely rework the vmemmap_populate_compound() to avoid the sparse_add_section
   hack into passing block across sparse_add_section calls. It's a lot easier to
   follow and more explicit in what it does.
 * Replace the vmemmap refactoring with adding a @pgmap argument and moving
   parts of the vmemmap_populate_base_pages(). (Patch 5 and 6 are new as a result)
 * Add PMD tail page vmemmap area reuse for 1GB pages. (Patch 8 is new)
 * Improve memmap_init_zone_device() to initialize compound pages when
   struct pages are cache warm. That lead to a even further speed up further
   from RFC series from 190ms -> 80-120ms. Patches 2 and 3 are the new ones
   as a result (Dan)
 * Remove PGMAP_COMPOUND and use @align as the property to detect whether
   or not to reuse vmemmap areas (Dan)

[0] https://lore.kernel.org/linux-mm/[e-mail]/
[1] https://lore.kernel.org/linux-mm/[e-mail]/
[2] https://lore.kernel.org/linux-mm/[e-mail]/
[3] https://lore.kernel.org/linux-mm/[e-mail]/
[4] https://lore.kernel.org/linux-mm/[e-mail]/
[5] https://lore.kernel.org/linux-mm/[e-mail]/
[6] https://lore.kernel.org/linux-mm/[e-mail]/
[7] https://lore.kernel.org/linux-mm/[e-mail]/
[8] https://lore.kernel.org/linux-mm/[e-mail]/
[9] https://lore.kernel.org/linux-mm/[e-mail]/
[10] https://lore.kernel.org/linux-mm/[e-mail]/

Joao Martins (11):
  memory-failure: fetch compound_head after pgmap_pfn_valid()
  mm/page_alloc: split prep_compound_page into head and tail subparts
  mm/page_alloc: refactor memmap_init_zone_device() page init
  mm/memremap: add ZONE_DEVICE support for compound pages
  device-dax: use ALIGN() for determining pgoff
  device-dax: use struct_size()
  device-dax: ensure dev_dax->pgmap is valid for dynamic devices
  device-dax: factor out page mapping initialization
  device-dax: set mapping prior to vmf_insert_pfn{,_pmd,pud}()
  device-dax: remove pfn from __dev_dax_{pte,pmd,pud}_fault()
  device-dax: compound devmap support

 drivers/dax/bus.c        |  32 +++++++++
 drivers/dax/bus.h        |   1 +
 drivers/dax/device.c     | 124 +++++++++++++++++++++--------------
 include/linux/memremap.h |  11 ++++
 mm/memory-failure.c      |   6 ++
 mm/memremap.c            |  18 +++--
 mm/page_alloc.c          | 138 +++++++++++++++++++++++++++------------
 7 files changed, 233 insertions(+), 97 deletions(-)