linux.git/mm/filemap.c, branch v6.6-rc2

mm: memory-failure: use rcu lock instead of tasklist_lock when collect_procs()

2023-09-05T18:11:52+00:00

We found a softlock issue in our test, analyzed the logs, and found that
the relevant CPU call trace as follows:

CPU0:
  _do_fork
    -> copy_process()
      -> write_lock_irq(&tasklist_lock)  //Disable irq,waiting for
      					 //tasklist_lock

CPU1:
  wp_page_copy()
    ->pte_offset_map_lock()
      -> spin_lock(&page->ptl);        //Hold page->ptl
    -> ptep_clear_flush()
      -> flush_tlb_others() ...
        -> smp_call_function_many()
          -> arch_send_call_function_ipi_mask()
            -> csd_lock_wait()         //Waiting for other CPUs respond
	                               //IPI

CPU2:
  collect_procs_anon()
    -> read_lock(&tasklist_lock)       //Hold tasklist_lock
      ->for_each_process(tsk)
        -> page_mapped_in_vma()
          -> page_vma_mapped_walk()
	    -> map_pte()
              ->spin_lock(&page->ptl)  //Waiting for page->ptl

We can see that CPU1 waiting for CPU0 respond IPI，CPU0 waiting for CPU2
unlock tasklist_lock, CPU2 waiting for CPU1 unlock page->ptl. As a result,
softlockup is triggered.

For collect_procs_anon(), what we're doing is task list iteration, during
the iteration, with the help of call_rcu(), the task_struct object is freed
only after one or more grace periods elapse. the logic as follows:

release_task()
  -> __exit_signal()
    -> __unhash_process()
      -> list_del_rcu()

  -> put_task_struct_rcu_user()
    -> call_rcu(&task->rcu, delayed_put_task_struct)

delayed_put_task_struct()
  -> put_task_struct()
  -> if (refcount_sub_and_test())
     	__put_task_struct()
          -> free_task()

Therefore, under the protection of the rcu lock, we can safely use
get_task_struct() to ensure a safe reference to task_struct during the
iteration.

By removing the use of tasklist_lock in task list iteration, we can break
the softlock chain above.

The same logic can also be applied to:
 - collect_procs_file()
 - collect_procs_fsdax()
 - collect_procs_ksm()

Link: https://lkml.kernel.org/r/20230828022527.241693-1-tongtiangen@huawei.com
Signed-off-by: Tong Tiangen 
Acked-by: Naoya Horiguchi 
Cc: Kefeng Wang 
Cc: Matthew Wilcox (Oracle) 
Cc: Miaohe Lin 
Cc: Paul E. McKenney 
Signed-off-by: Andrew Morton

Merge tag 'mm-stable-2023-08-28-18-26' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2023-08-29T21:25:26+00:00

Pull MM updates from Andrew Morton:

 - Some swap cleanups from Ma Wupeng ("fix WARN_ON in
   add_to_avail_list")

 - Peter Xu has a series (mm/gup: Unify hugetlb, speed up thp") which
   reduces the special-case code for handling hugetlb pages in GUP. It
   also speeds up GUP handling of transparent hugepages.

 - Peng Zhang provides some maple tree speedups ("Optimize the fast path
   of mas_store()").

 - Sergey Senozhatsky has improved te performance of zsmalloc during
   compaction (zsmalloc: small compaction improvements").

 - Domenico Cerasuolo has developed additional selftest code for zswap
   ("selftests: cgroup: add zswap test program").

 - xu xin has doe some work on KSM's handling of zero pages. These
   changes are mainly to enable the user to better understand the
   effectiveness of KSM's treatment of zero pages ("ksm: support
   tracking KSM-placed zero-pages").

 - Jeff Xu has fixes the behaviour of memfd's
   MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED sysctl ("mm/memfd: fix sysctl
   MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED").

 - David Howells has fixed an fscache optimization ("mm, netfs, fscache:
   Stop read optimisation when folio removed from pagecache").

 - Axel Rasmussen has given userfaultfd the ability to simulate memory
   poisoning ("add UFFDIO_POISON to simulate memory poisoning with
   UFFD").

 - Miaohe Lin has contributed some routine maintenance work on the
   memory-failure code ("mm: memory-failure: remove unneeded PageHuge()
   check").

 - Peng Zhang has contributed some maintenance work on the maple tree
   code ("Improve the validation for maple tree and some cleanup").

 - Hugh Dickins has optimized the collapsing of shmem or file pages into
   THPs ("mm: free retracted page table by RCU").

 - Jiaqi Yan has a patch series which permits us to use the healthy
   subpages within a hardware poisoned huge page for general purposes
   ("Improve hugetlbfs read on HWPOISON hugepages").

 - Kemeng Shi has done some maintenance work on the pagetable-check code
   ("Remove unused parameters in page_table_check").

 - More folioification work from Matthew Wilcox ("More filesystem folio
   conversions for 6.6"), ("Followup folio conversions for zswap"). And
   from ZhangPeng ("Convert several functions in page_io.c to use a
   folio").

 - page_ext cleanups from Kemeng Shi ("minor cleanups for page_ext").

 - Baoquan He has converted some architectures to use the
   GENERIC_IOREMAP ioremap()/iounmap() code ("mm: ioremap: Convert
   architectures to take GENERIC_IOREMAP way").

 - Anshuman Khandual has optimized arm64 tlb shootdown ("arm64: support
   batched/deferred tlb shootdown during page reclamation/migration").

 - Better maple tree lockdep checking from Liam Howlett ("More strict
   maple tree lockdep"). Liam also developed some efficiency
   improvements ("Reduce preallocations for maple tree").

 - Cleanup and optimization to the secondary IOMMU TLB invalidation,
   from Alistair Popple ("Invalidate secondary IOMMU TLB on permission
   upgrade").

 - Ryan Roberts fixes some arm64 MM selftest issues ("selftests/mm fixes
   for arm64").

 - Kemeng Shi provides some maintenance work on the compaction code
   ("Two minor cleanups for compaction").

 - Some reduction in mmap_lock pressure from Matthew Wilcox ("Handle
   most file-backed faults under the VMA lock").

 - Aneesh Kumar contributes code to use the vmemmap optimization for DAX
   on ppc64, under some circumstances ("Add support for DAX vmemmap
   optimization for ppc64").

 - page-ext cleanups from Kemeng Shi ("add page_ext_data to get client
   data in page_ext"), ("minor cleanups to page_ext header").

 - Some zswap cleanups from Johannes Weiner ("mm: zswap: three
   cleanups").

 - kmsan cleanups from ZhangPeng ("minor cleanups for kmsan").

 - VMA handling cleanups from Kefeng Wang ("mm: convert to
   vma_is_initial_heap/stack()").

 - DAMON feature work from SeongJae Park ("mm/damon/sysfs-schemes:
   implement DAMOS tried total bytes file"), ("Extend DAMOS filters for
   address ranges and DAMON monitoring targets").

 - Compaction work from Kemeng Shi ("Fixes and cleanups to compaction").

 - Liam Howlett has improved the maple tree node replacement code
   ("maple_tree: Change replacement strategy").

 - ZhangPeng has a general code cleanup - use the K() macro more widely
   ("cleanup with helper macro K()").

 - Aneesh Kumar brings memmap-on-memory to ppc64 ("Add support for
   memmap on memory feature on ppc64").

 - pagealloc cleanups from Kemeng Shi ("Two minor cleanups for pcp list
   in page_alloc"), ("Two minor cleanups for get pageblock
   migratetype").

 - Vishal Moola introduces a memory descriptor for page table tracking,
   "struct ptdesc" ("Split ptdesc from struct page").

 - memfd selftest maintenance work from Aleksa Sarai ("memfd: cleanups
   for vm.memfd_noexec").

 - MM include file rationalization from Hugh Dickins ("arch: include
   asm/cacheflush.h in asm/hugetlb.h").

 - THP debug output fixes from Hugh Dickins ("mm,thp: fix sloppy text
   output").

 - kmemleak improvements from Xiaolei Wang ("mm/kmemleak: use
   object_cache instead of kmemleak_initialized").

 - More folio-related cleanups from Matthew Wilcox ("Remove _folio_dtor
   and _folio_order").

 - A VMA locking scalability improvement from Suren Baghdasaryan
   ("Per-VMA lock support for swap and userfaults").

 - pagetable handling cleanups from Matthew Wilcox ("New page table
   range API").

 - A batch of swap/thp cleanups from David Hildenbrand ("mm/swap: stop
   using page->private on tail pages for THP_SWAP + cleanups").

 - Cleanups and speedups to the hugetlb fault handling from Matthew
   Wilcox ("Change calling convention for ->huge_fault").

 - Matthew Wilcox has also done some maintenance work on the MM
   subsystem documentation ("Improve mm documentation").

* tag 'mm-stable-2023-08-28-18-26' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (489 commits)
  maple_tree: shrink struct maple_tree
  maple_tree: clean up mas_wr_append()
  secretmem: convert page_is_secretmem() to folio_is_secretmem()
  nios2: fix flush_dcache_page() for usage from irq context
  hugetlb: add documentation for vma_kernel_pagesize()
  mm: add orphaned kernel-doc to the rst files.
  mm: fix clean_record_shared_mapping_range kernel-doc
  mm: fix get_mctgt_type() kernel-doc
  mm: fix kernel-doc warning from tlb_flush_rmaps()
  mm: remove enum page_entry_size
  mm: allow ->huge_fault() to be called without the mmap_lock held
  mm: move PMD_ORDER to pgtable.h
  mm: remove checks for pte_index
  memcg: remove duplication detection for mem_cgroup_uncharge_swap
  mm/huge_memory: work on folio->swap instead of page->private when splitting folio
  mm/swap: inline folio_set_swap_entry() and folio_swap_entry()
  mm/swap: use dedicated entry for swap in folio
  mm/swap: stop using page->private on tail pages for THP_SWAP
  selftests/mm: fix WARNING comparing pointer to 0
  selftests: cgroup: fix test_kmem_memcg_deletion kernel mem check
  ...

filemap: batch PTE mappings

2023-08-24T23:20:26+00:00

Call set_pte_range() once per contiguous range of the folio instead of
once per page.  This batches the updates to mm counters and the rmap.

With a will-it-scale.page_fault3 like app (change file write fault testing
to read fault testing.  Trying to upstream it to will-it-scale at [1]) got
15% performance gain on a 48C/96T Cascade Lake test box with 96 processes
running against xfs.

Perf data collected before/after the change:
  18.73%--page_add_file_rmap
          |
           --11.60%--__mod_lruvec_page_state
                     |
                     |--7.40%--__mod_memcg_lruvec_state
                     |          |
                     |           --5.58%--cgroup_rstat_updated
                     |
                      --2.53%--__mod_lruvec_state
                                |
                                 --1.48%--__mod_node_page_state

  9.93%--page_add_file_rmap_range
         |
          --2.67%--__mod_lruvec_page_state
                    |
                    |--1.95%--__mod_memcg_lruvec_state
                    |          |
                    |           --1.57%--cgroup_rstat_updated
                    |
                     --0.61%--__mod_lruvec_state
                               |
                                --0.54%--__mod_node_page_state

The running time of __mode_lruvec_page_state() is reduced about 9%.

[1]: https://github.com/antonblanchard/will-it-scale/pull/37

Link: https://lkml.kernel.org/r/20230802151406.3735276-38-willy@infradead.org
Signed-off-by: Yin Fengwei 
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton

mm: convert do_set_pte() to set_pte_range()

2023-08-24T23:20:26+00:00

set_pte_range() allows to setup page table entries for a specific
range.  It takes advantage of batched rmap update for large folio.
It now takes care of calling update_mmu_cache_range().

Link: https://lkml.kernel.org/r/20230802151406.3735276-37-willy@infradead.org
Signed-off-by: Yin Fengwei 
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton

filemap: add filemap_map_folio_range()

2023-08-24T23:20:26+00:00

filemap_map_folio_range() maps partial/full folio.  Comparing to original
filemap_map_pages(), it updates refcount once per folio instead of per
page and gets minor performance improvement for large folio.

With a will-it-scale.page_fault3 like app (change file write fault testing
to read fault testing.  Trying to upstream it to will-it-scale at [1]),
got 2% performance gain on a 48C/96T Cascade Lake test box with 96
processes running against xfs.

[1]: https://github.com/antonblanchard/will-it-scale/pull/37

Link: https://lkml.kernel.org/r/20230802151406.3735276-35-willy@infradead.org
Signed-off-by: Yin Fengwei 
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton

mm: handle swap page faults under per-VMA lock

2023-08-24T23:20:17+00:00

When page fault is handled under per-VMA lock protection, all swap page
faults are retried with mmap_lock because folio_lock_or_retry has to drop
and reacquire mmap_lock if folio could not be immediately locked.  Follow
the same pattern as mmap_lock to drop per-VMA lock when waiting for folio
and retrying once folio is available.

With this obstacle removed, enable do_swap_page to operate under per-VMA
lock protection.  Drivers implementing ops->migrate_to_ram might still
rely on mmap_lock, therefore we have to fall back to mmap_lock in that
particular case.

Note that the only time do_swap_page calls synchronous swap_readpage is
when SWP_SYNCHRONOUS_IO is set, which is only set for
QUEUE_FLAG_SYNCHRONOUS devices: brd, zram and nvdimms (both btt and pmem).
Therefore we don't sleep in this path, and there's no need to drop the
mmap or per-VMA lock.

Link: https://lkml.kernel.org/r/20230630211957.1341547-6-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Tested-by: Alistair Popple 
Reviewed-by: Alistair Popple 
Acked-by: Peter Xu 
Cc: Al Viro 
Cc: Christian Brauner 
Cc: Christoph Hellwig 
Cc: David Hildenbrand 
Cc: David Howells 
Cc: Davidlohr Bueso 
Cc: Hillf Danton 
Cc: "Huang, Ying" 
Cc: Hugh Dickins 
Cc: Jan Kara 
Cc: Johannes Weiner 
Cc: Josef Bacik 
Cc: Laurent Dufour 
Cc: Liam R. Howlett 
Cc: Lorenzo Stoakes 
Cc: Matthew Wilcox 
Cc: Michal Hocko 
Cc: Michel Lespinasse 
Cc: Minchan Kim 
Cc: Pavel Tatashin 
Cc: Punit Agrawal 
Cc: Vlastimil Babka 
Cc: Yu Zhao 
Signed-off-by: Andrew Morton

mm: change folio_lock_or_retry to use vm_fault directly

2023-08-24T23:20:17+00:00

Change folio_lock_or_retry to accept vm_fault struct and return the
vm_fault_t directly.

Link: https://lkml.kernel.org/r/20230630211957.1341547-5-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Suggested-by: Matthew Wilcox 
Acked-by: Peter Xu 
Cc: Alistair Popple 
Cc: Al Viro 
Cc: Christian Brauner 
Cc: Christoph Hellwig 
Cc: David Hildenbrand 
Cc: David Howells 
Cc: Davidlohr Bueso 
Cc: Hillf Danton 
Cc: "Huang, Ying" 
Cc: Hugh Dickins 
Cc: Jan Kara 
Cc: Johannes Weiner 
Cc: Josef Bacik 
Cc: Laurent Dufour 
Cc: Liam R. Howlett 
Cc: Lorenzo Stoakes 
Cc: Michal Hocko 
Cc: Michel Lespinasse 
Cc: Minchan Kim 
Cc: Pavel Tatashin 
Cc: Punit Agrawal 
Cc: Vlastimil Babka 
Cc: Yu Zhao 
Signed-off-by: Andrew Morton

mm: merge folio_has_private()/filemap_release_folio() call pairs

2023-08-18T17:12:12+00:00

Patch series "mm, netfs, fscache: Stop read optimisation when folio
removed from pagecache", v7.

This fixes an optimisation in fscache whereby we don't read from the cache
for a particular file until we know that there's data there that we don't
have in the pagecache.  The problem is that I'm no longer using PG_fscache
(aka PG_private_2) to indicate that the page is cached and so I don't get
a notification when a cached page is dropped from the pagecache.

The first patch merges some folio_has_private() and
filemap_release_folio() pairs and introduces a helper,
folio_needs_release(), to indicate if a release is required.

The second patch is the actual fix.  Following Willy's suggestions[1], it
adds an AS_RELEASE_ALWAYS flag to an address_space that will make
filemap_release_folio() always call ->release_folio(), even if
PG_private/PG_private_2 aren't set.  folio_needs_release() is altered to
add a check for this.


This patch (of 2):

Make filemap_release_folio() check folio_has_private().  Then, in most
cases, where a call to folio_has_private() is immediately followed by a
call to filemap_release_folio(), we can get rid of the test in the pair.

There are a couple of sites in mm/vscan.c that this can't so easily be
done.  In shrink_folio_list(), there are actually three cases (something
different is done for incompletely invalidated buffers), but
filemap_release_folio() elides two of them.

In shrink_active_list(), we don't have have the folio lock yet, so the
check allows us to avoid locking the page unnecessarily.

A wrapper function to check if a folio needs release is provided for those
places that still need to do it in the mm/ directory.  This will acquire
additional parts to the condition in a future patch.

After this, the only remaining caller of folio_has_private() outside of
mm/ is a check in fuse.

Link: https://lkml.kernel.org/r/20230628104852.3391651-1-dhowells@redhat.com
Link: https://lkml.kernel.org/r/20230628104852.3391651-2-dhowells@redhat.com
Reported-by: Rohith Surabattula 
Suggested-by: Matthew Wilcox 
Signed-off-by: David Howells 
Cc: Matthew Wilcox 
Cc: Linus Torvalds 
Cc: Steve French 
Cc: Shyam Prasad N 
Cc: Rohith Surabattula 
Cc: Dave Wysochanski 
Cc: Dominique Martinet 
Cc: Ilya Dryomov 
Cc: "Theodore Ts'o" 
Cc: Andreas Dilger 
Cc: Xiubo Li 
Cc: Jingbo Xu 
Signed-off-by: Andrew Morton

mm/filemap.c: fix update prev_pos after one read request done

2023-08-18T17:12:04+00:00

ra->prev_pos tracks the last visited byte in the previous read request. 
It is used to check whether it is sequential read in ondemand_readahead
and thus affects the readahead window.

After commit 06c0444290ce ("mm/filemap.c: generic_file_buffered_read() now
uses find_get_pages_contig"), update logic of prev_pos is changed.  It
updates prev_pos after each return from filemap_get_pages().  But the read
request from user may be not fully completed at this point.  The updated
prev_pos impacts the subsequent readahead window.

The real problem is performance drop of fsck_msdos between linux-5.4 and
linux-5.15(also linux-6.4).  Comparing to linux-5.4,It spends about 110%
time and read 140% pages.  The read pattern of fsck_msdos is not fully
sequential.

Simplified read pattern of fsck_msdos likes below:
1.read at page offset 0xa,size 0x1000
2.read at other page offset like 0x20,size 0x1000
3.read at page offset 0xa,size 0x4000
4.read at page offset 0xe,size 0x1000

Here is the read status on linux-6.4:
1.after read at page offset 0xa,size 0x1000
    ->page ofs 0xa go into pagecache
2.after read at page offset 0x20,size 0x1000
    ->page ofs 0x20 go into pagecache
3.read at page offset 0xa,size 0x4000
    ->filemap_get_pages read ofs 0xa from pagecache and returns
    ->prev_pos is updated to 0xb and goto next loop
    ->filemap_get_pages tends to read ofs 0xb,size 0x3000
    ->initial_readahead case in ondemand_readahead since prev_pos is
      the same as request ofs.
    ->read 8 pages while async size is 5 pages
      (PageReadahead flag at page 0xe)
4.read at page offset 0xe,size 0x1000
    ->hit page 0xe with PageReadahead flag set,double the ra_size.
      read 16 pages while async size is 16 pages
Now it reads 24 pages while actually uses 5 pages

on linux-5.4:
1.the same as 6.4
2.the same as 6.4
3.read at page offset 0xa,size 0x4000
    ->read ofs 0xa from pagecache
    ->read ofs 0xb,size 0x3000 using page_cache_sync_readahead
      read 3 pages
    ->prev_pos is updated to 0xd before generic_file_buffered_read
      returns
4.read at page offset 0xe,size 0x1000
    ->initial_readahead case in ondemand_readahead since
      request ofs-prev_pos==1
    ->read 4 pages while async size is 3 pages

Now it reads 7 pages while actually uses 5 pages.

In above demo, the initial_readahead case is triggered by offset of user
request on linux-5.4.  While it may be triggered by update logic of
prev_pos on linux-6.4.

To fix the performance drop, update prev_pos after finishing one read
request.

Link: https://lkml.kernel.org/r/20230628110220.120134-1-haibo.li@mediatek.com
Signed-off-by: Haibo Li 
Reviewed-by: Jan Kara 
Cc: AngeloGioacchino Del Regno 
Cc: Matthew Wilcox 
Cc: Matthias Brugger 
Signed-off-by: Andrew Morton

mm: increase usage of folio_next_index() helper

2023-08-18T17:12:00+00:00

Simplify code pattern of 'folio->index + folio_nr_pages(folio)' by using
the existing helper folio_next_index().

Link: https://lkml.kernel.org/r/20230627174349.491803-1-sidhartha.kumar@oracle.com
Signed-off-by: Sidhartha Kumar 
Suggested-by: Christoph Hellwig 
Reviewed-by: Christoph Hellwig 
Cc: Andreas Dilger 
Cc: Christoph Hellwig 
Cc: Hugh Dickins 
Cc: Matthew Wilcox 
Cc: Theodore Ts'o 
Signed-off-by: Andrew Morton