linux.git/include/linux/pagemap.h, branch v5.2-rc4

mm: delete find_get_entries_tag

2019-05-14T16:47:51+00:00

I removed the only user of this and hadn't noticed it was now unused.

Link: http://lkml.kernel.org/r/20190430152929.21813-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Reviewed-by: Ross Zwisler 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/page-writeback: introduce tracepoint for wait_on_page_writeback()

2019-05-14T16:47:51+00:00

Recently there have been some hung tasks on our server due to
wait_on_page_writeback(), and we want to know the details of this
PG_writeback, i.e.  this page is writing back to which device.  But it is
not so convenient to get the details.

I think it would be better to introduce a tracepoint for diagnosing the
writeback details.

Link: http://lkml.kernel.org/r/1556274402-19018-1-git-send-email-laoar.shao@gmail.com
Signed-off-by: Yafang Shao 
Reviewed-by: Andrew Morton 
Cc: Jan Kara 
Cc: Michal Hocko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: page cache: store only head pages in i_pages

2019-05-14T16:47:45+00:00

Transparent Huge Pages are currently stored in i_pages as pointers to
consecutive subpages.  This patch changes that to storing consecutive
pointers to the head page in preparation for storing huge pages more
efficiently in i_pages.

Large parts of this are "inspired" by Kirill's patch
https://lore.kernel.org/lkml/20170126115819.58875-2-kirill.shutemov@linux.intel.com/

[willy@infradead.org: fix swapcache pages]
  Link: http://lkml.kernel.org/r/20190324155441.GF10344@bombadil.infradead.org
[kirill@shutemov.name: hugetlb stores pages in page cache differently]
  Link: http://lkml.kernel.org/r/20190404134553.vuvhgmghlkiw2hgl@kshutemo-mobl1
Link: http://lkml.kernel.org/r/20190307153051.18815-1-willy@infradead.org
Signed-off-by: Matthew Wilcox 
Acked-by: Jan Kara 
Reviewed-by: Kirill Shutemov 
Reviewed-and-tested-by: Song Liu 
Tested-by: William Kucharski 
Reviewed-by: William Kucharski 
Tested-by: Qian Cai 
Cc: Hugh Dickins 
Cc: Song Liu 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

filemap: kill page_cache_read usage in filemap_fault

2019-03-15T18:21:25+00:00

Patch series "drop the mmap_sem when doing IO in the fault path", v6.

Now that we have proper isolation in place with cgroups2 we have started
going through and fixing the various priority inversions.  Most are all
gone now, but this one is sort of weird since it's not necessarily a
priority inversion that happens within the kernel, but rather because of
something userspace does.

We have giant applications that we want to protect, and parts of these
giant applications do things like watch the system state to determine how
healthy the box is for load balancing and such.  This involves running
'ps' or other such utilities.  These utilities will often walk
/proc//whatever, and these files can sometimes need to
down_read(&task->mmap_sem).  Not usually a big deal, but we noticed when
we are stress testing that sometimes our protected application has latency
spikes trying to get the mmap_sem for tasks that are in lower priority
cgroups.

This is because any down_write() on a semaphore essentially turns it into
a mutex, so even if we currently have it held for reading, any new readers
will not be allowed on to keep from starving the writer.  This is fine,
except a lower priority task could be stuck doing IO because it has been
throttled to the point that its IO is taking much longer than normal.  But
because a higher priority group depends on this completing it is now stuck
behind lower priority work.

In order to avoid this particular priority inversion we want to use the
existing retry mechanism to stop from holding the mmap_sem at all if we
are going to do IO.  This already exists in the read case sort of, but
needed to be extended for more than just grabbing the page lock.  With
io.latency we throttle at submit_bio() time, so the readahead stuff can
block and even page_cache_read can block, so all these paths need to have
the mmap_sem dropped.

The other big thing is ->page_mkwrite.  btrfs is particularly shitty here
because we have to reserve space for the dirty page, which can be a very
expensive operation.  We use the same retry method as the read path, and
simply cache the page and verify the page is still setup properly the next
pass through ->page_mkwrite().

I've tested these patches with xfstests and there are no regressions.

This patch (of 3):

If we do not have a page at filemap_fault time we'll do this weird forced
page_cache_read thing to populate the page, and then drop it again and
loop around and find it.  This makes for 2 ways we can read a page in
filemap_fault, and it's not really needed.  Instead add a FGP_FOR_MMAP
flag so that pagecache_get_page() will return a unlocked page that's in
pagecache.  Then use the normal page locking and readpage logic already in
filemap_fault.  This simplifies the no page in page cache case
significantly.

[akpm@linux-foundation.org: fix comment text]
[josef@toxicpanda.com: don't unlock null page in FGP_FOR_MMAP case]
  Link: http://lkml.kernel.org/r/20190312201742.22935-1-josef@toxicpanda.com
Link: http://lkml.kernel.org/r/20181211173801.29535-2-josef@toxicpanda.com
Signed-off-by: Josef Bacik 
Acked-by: Johannes Weiner 
Reviewed-by: Jan Kara 
Reviewed-by: Andrew Morton 
Cc: Tejun Heo 
Cc: Dave Chinner 
Cc: Rik van Riel 
Cc: "Kirill A. Shutemov" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: page_cache_add_speculative(): refactor out some code duplication

2019-03-06T05:07:20+00:00

From: John Hubbard 

This combines the common elements of these routines:

    page_cache_get_speculative()
    page_cache_add_speculative()

This was anticipated by the original author, as shown by the comment in
commit ce0ad7f095258 ("powerpc/mm: Lockless get_user_pages_fast() for
64-bit (v3)"):

    "Same as above, but add instead of inc (could just be merged)"

There is no intention to introduce any behavioral change, but there is a
small risk of that, due to slightly differing ways of expressing the
TINY_RCU and related configurations.

This also removes the VM_BUG_ON(in_interrupt()) that was in
page_cache_add_speculative(), but not in page_cache_get_speculative().
This provides slightly less detection of such bugs, but it given that it
was only there on the "add" path anyway, we can likely do without it
just fine.

And it removes the
VM_BUG_ON_PAGE(PageCompound(page) && page != compound_head(page), page);
that page_cache_add_speculative() had.

Link: http://lkml.kernel.org/r/20190206231016.22734-2-jhubbard@nvidia.com
Signed-off-by: John Hubbard 
Reviewed-by: Andrew Morton 
Cc: Benjamin Herrenschmidt 
Cc: Dave Kleikamp 
Cc: Hugh Dickins 
Cc: Jeff Layton 
Cc: Matthew Wilcox 
Cc: Nicholas Piggin 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: put_and_wait_on_page_locked() while page is migrated

2018-12-28T20:11:48+00:00

Waiting on a page migration entry has used wait_on_page_locked() all along
since 2006: but you cannot safely wait_on_page_locked() without holding a
reference to the page, and that extra reference is enough to make
migrate_page_move_mapping() fail with -EAGAIN, when a racing task faults
on the entry before migrate_page_move_mapping() gets there.

And that failure is retried nine times, amplifying the pain when trying to
migrate a popular page.  With a single persistent faulter, migration
sometimes succeeds; with two or three concurrent faulters, success becomes
much less likely (and the more the page was mapped, the worse the overhead
of unmapping and remapping it on each try).

This is especially a problem for memory offlining, where the outer level
retries forever (or until terminated from userspace), because a heavy
refault workload can trigger an endless loop of migration failures.
wait_on_page_locked() is the wrong tool for the job.

David Herrmann (but was he the first?) noticed this issue in 2014:
https://marc.info/?l=linux-mm&m=140110465608116&w=2

Tim Chen started a thread in August 2017 which appears relevant:
https://marc.info/?l=linux-mm&m=150275941014915&w=2 where Kan Liang went
on to implicate __migration_entry_wait():
https://marc.info/?l=linux-mm&m=150300268411980&w=2 and the thread ended
up with the v4.14 commits: 2554db916586 ("sched/wait: Break up long wake
list walk") 11a19c7b099f ("sched/wait: Introduce wakeup boomark in
wake_up_page_bit")

Baoquan He reported "Memory hotplug softlock issue" 14 November 2018:
https://marc.info/?l=linux-mm&m=154217936431300&w=2

We have all assumed that it is essential to hold a page reference while
waiting on a page lock: partly to guarantee that there is still a struct
page when MEMORY_HOTREMOVE is configured, but also to protect against
reuse of the struct page going to someone who then holds the page locked
indefinitely, when the waiter can reasonably expect timely unlocking.

But in fact, so long as wait_on_page_bit_common() does the put_page(), and
is careful not to rely on struct page contents thereafter, there is no
need to hold a reference to the page while waiting on it.  That does mean
that this case cannot go back through the loop: but that's fine for the
page migration case, and even if used more widely, is limited by the "Stop
walking if it's locked" optimization in wake_page_function().

Add interface put_and_wait_on_page_locked() to do this, using "behavior"
enum in place of "lock" arg to wait_on_page_bit_common() to implement it.
No interruptible or killable variant needed yet, but they might follow: I
have a vague notion that reporting -EINTR should take precedence over
return from wait_on_page_bit_common() without knowing the page state, so
arrange it accordingly - but that may be nothing but pedantic.

__migration_entry_wait() still has to take a brief reference to the page,
prior to calling put_and_wait_on_page_locked(): but now that it is dropped
before waiting, the chance of impeding page migration is very much
reduced.  Should we perhaps disable preemption across this?

shrink_page_list()'s __ClearPageLocked(): that was a surprise!  This
survived a lot of testing before that showed up.  PageWaiters may have
been set by wait_on_page_bit_common(), and the reference dropped, just
before shrink_page_list() succeeds in freezing its last page reference: in
such a case, unlock_page() must be used.  Follow the suggestion from
Michal Hocko, just revert a978d6f52106 ("mm: unlockless reclaim") now:
that optimization predates PageWaiters, and won't buy much these days; but
we can reinstate it for the !PageWaiters case if anyone notices.

It does raise the question: should vmscan.c's is_page_cache_freeable() and
__remove_mapping() now treat a PageWaiters page as if an extra reference
were held?  Perhaps, but I don't think it matters much, since
shrink_page_list() already had to win its trylock_page(), so waiters are
not very common there: I noticed no difference when trying the bigger
change, and it's surely not needed while put_and_wait_on_page_locked() is
only used for page migration.

[willy@infradead.org: add put_and_wait_on_page_locked() kerneldoc]
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261121330.1116@eggly.anvils
Signed-off-by: Hugh Dickins 
Reported-by: Baoquan He 
Tested-by: Baoquan He 
Reviewed-by: Andrea Arcangeli 
Acked-by: Michal Hocko 
Acked-by: Linus Torvalds 
Acked-by: Vlastimil Babka 
Cc: Matthew Wilcox 
Cc: Baoquan He 
Cc: David Hildenbrand 
Cc: Mel Gorman 
Cc: David Herrmann 
Cc: Tim Chen 
Cc: Kan Liang 
Cc: Andi Kleen 
Cc: Davidlohr Bueso 
Cc: Peter Zijlstra 
Cc: Christoph Lameter 
Cc: Nick Piggin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

page cache: Convert find_get_entries_tag to XArray

2018-10-21T14:46:35+00:00

Slightly shorter and simpler code.

Signed-off-by: Matthew Wilcox

page cache; Convert find_get_pages_range_tag to XArray

2018-10-21T14:46:35+00:00

The 'end' parameter of the xas_for_each iterator avoids a useless
iteration at the end of the range.

Signed-off-by: Matthew Wilcox

page cache: Convert hole search to XArray

2018-10-21T14:46:33+00:00

The page cache offers the ability to search for a miss in the previous or
next N locations.  Rather than teach the XArray about the page cache's
definition of a miss, use xas_prev() and xas_next() to search the page
array.  This should be more efficient as it does not have to start the
lookup from the top for each index.

Signed-off-by: Matthew Wilcox

page cache: use xa_lock

2018-04-11T17:28:39+00:00

Remove the address_space ->tree_lock and use the xa_lock newly added to
the radix_tree_root.  Rename the address_space ->page_tree to ->i_pages,
since we don't really care that it's a tree.

[willy@infradead.org: fix nds32, fs/dax.c]
  Link: http://lkml.kernel.org/r/20180406145415.GB20605@bombadil.infradead.orgLink: http://lkml.kernel.org/r/20180313132639.17387-9-willy@infradead.org
Signed-off-by: Matthew Wilcox 
Acked-by: Jeff Layton 
Cc: Darrick J. Wong 
Cc: Dave Chinner 
Cc: Ryusuke Konishi 
Cc: Will Deacon 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds