linux-stable.git/mm/internal.h, branch linux-5.7.y

mm: add function __putback_isolated_page

2020-04-07T17:43:38+00:00

There are cases where we would benefit from avoiding having to go through
the allocation and free cycle to return an isolated page.

Examples for this might include page poisoning in which we isolate a page
and then put it back in the free list without ever having actually
allocated it.

This will enable us to also avoid notifiers for the future free page
reporting which will need to avoid retriggering page reporting when
returning pages that have been reported on.

Signed-off-by: Alexander Duyck 
Signed-off-by: Andrew Morton 
Acked-by: David Hildenbrand 
Acked-by: Mel Gorman 
Cc: Andrea Arcangeli 
Cc: Dan Williams 
Cc: Dave Hansen 
Cc: Konrad Rzeszutek Wilk 
Cc: Luiz Capitulino 
Cc: Matthew Wilcox 
Cc: Michael S. Tsirkin 
Cc: Michal Hocko 
Cc: Nitesh Narayan Lal 
Cc: Oscar Salvador 
Cc: Pankaj Gupta 
Cc: Paolo Bonzini 
Cc: Rik van Riel 
Cc: Vlastimil Babka 
Cc: Wei Wang 
Cc: Yang Zhang 
Cc: wei qi 
Link: http://lkml.kernel.org/r/20200211224624.29318.89287.stgit@localhost.localdomain
Signed-off-by: Linus Torvalds

mm,compaction,cma: add alloc_contig flag to compact_control

2020-04-02T16:35:31+00:00

Patch series "fix THP migration for CMA allocations", v2.

Transparent huge pages are allocated with __GFP_MOVABLE, and can end up in
CMA memory blocks.  Transparent huge pages also have most of the
infrastructure in place to allow migration.

However, a few pieces were missing, causing THP migration to fail when
attempting to use CMA to allocate 1GB hugepages.

With these patches in place, THP migration from CMA blocks seems to work,
both for anonymous THPs and for tmpfs/shmem THPs.

This patch (of 2):

Add information to struct compact_control to indicate that the allocator
would really like to clear out this specific part of memory, used by for
example CMA.

Signed-off-by: Rik van Riel 
Signed-off-by: Andrew Morton 
Reviewed-by: Vlastimil Babka 
Cc: Andrea Arcangeli 
Cc: David Rientjes 
Cc: Mel Gorman 
Cc: Michal Hocko 
Cc: Zi Yan 
Cc: Joonsoo Kim 
Link: http://lkml.kernel.org/r/20200227213238.1298752-1-riel@surriel.com
Signed-off-by: Linus Torvalds

mm, pagealloc: micro-optimisation: save two branches on hot page allocation path

2020-04-02T16:35:30+00:00

This patch makes ALLOC_KSWAPD equal to __GFP_KSWAPD_RECLAIM (cast to int).

Thanks to that code like:

    if (gfp_mask & __GFP_KSWAPD_RECLAIM)
	    alloc_flags |= ALLOC_KSWAPD;

can be changed to:

    alloc_flags |= (__force int) (gfp_mask &__GFP_KSWAPD_RECLAIM);

Thanks to this one branch less is generated in the assembly.

In case of ALLOC_KSWAPD flag two branches are saved, first one in code
that always executes in the beginning of page allocation and the second
one in loop in page allocator slowpath.

Signed-off-by: Mateusz Nosek 
Signed-off-by: Andrew Morton 
Acked-by: Vlastimil Babka 
Acked-by: Mel Gorman 
Link: http://lkml.kernel.org/r/20200304162118.14784-1-mateusznosek0@gmail.com
Signed-off-by: Linus Torvalds

mm: allow VM_FAULT_RETRY for multiple times

2020-04-02T16:35:30+00:00

The idea comes from a discussion between Linus and Andrea [1].

Before this patch we only allow a page fault to retry once.  We achieved
this by clearing the FAULT_FLAG_ALLOW_RETRY flag when doing
handle_mm_fault() the second time.  This was majorly used to avoid
unexpected starvation of the system by looping over forever to handle the
page fault on a single page.  However that should hardly happen, and after
all for each code path to return a VM_FAULT_RETRY we'll first wait for a
condition (during which time we should possibly yield the cpu) to happen
before VM_FAULT_RETRY is really returned.

This patch removes the restriction by keeping the FAULT_FLAG_ALLOW_RETRY
flag when we receive VM_FAULT_RETRY.  It means that the page fault handler
now can retry the page fault for multiple times if necessary without the
need to generate another page fault event.  Meanwhile we still keep the
FAULT_FLAG_TRIED flag so page fault handler can still identify whether a
page fault is the first attempt or not.

Then we'll have these combinations of fault flags (only considering
ALLOW_RETRY flag and TRIED flag):

  - ALLOW_RETRY and !TRIED:  this means the page fault allows to
                             retry, and this is the first try

  - ALLOW_RETRY and TRIED:   this means the page fault allows to
                             retry, and this is not the first try

  - !ALLOW_RETRY and !TRIED: this means the page fault does not allow
                             to retry at all

  - !ALLOW_RETRY and TRIED:  this is forbidden and should never be used

In existing code we have multiple places that has taken special care of
the first condition above by checking against (fault_flags &
FAULT_FLAG_ALLOW_RETRY).  This patch introduces a simple helper to detect
the first retry of a page fault by checking against both (fault_flags &
FAULT_FLAG_ALLOW_RETRY) and !(fault_flag & FAULT_FLAG_TRIED) because now
even the 2nd try will have the ALLOW_RETRY set, then use that helper in
all existing special paths.  One example is in __lock_page_or_retry(), now
we'll drop the mmap_sem only in the first attempt of page fault and we'll
keep it in follow up retries, so old locking behavior will be retained.

This will be a nice enhancement for current code [2] at the same time a
supporting material for the future userfaultfd-writeprotect work, since in
that work there will always be an explicit userfault writeprotect retry
for protected pages, and if that cannot resolve the page fault (e.g., when
userfaultfd-writeprotect is used in conjunction with swapped pages) then
we'll possibly need a 3rd retry of the page fault.  It might also benefit
other potential users who will have similar requirement like userfault
write-protection.

GUP code is not touched yet and will be covered in follow up patch.

Please read the thread below for more information.

[1] https://lore.kernel.org/lkml/20171102193644.GB22686@redhat.com/
[2] https://lore.kernel.org/lkml/20181230154648.GB9832@redhat.com/

Suggested-by: Linus Torvalds 
Suggested-by: Andrea Arcangeli 
Signed-off-by: Peter Xu 
Signed-off-by: Andrew Morton 
Tested-by: Brian Geffon 
Cc: Bobby Powers 
Cc: David Hildenbrand 
Cc: Denis Plotnikov 
Cc: "Dr . David Alan Gilbert" 
Cc: Hugh Dickins 
Cc: Jerome Glisse 
Cc: Johannes Weiner 
Cc: "Kirill A . Shutemov" 
Cc: Martin Cracauer 
Cc: Marty McFadden 
Cc: Matthew Wilcox 
Cc: Maya Gokhale 
Cc: Mel Gorman 
Cc: Mike Kravetz 
Cc: Mike Rapoport 
Cc: Pavel Emelyanov 
Link: http://lkml.kernel.org/r/20200220160246.9790-1-peterx@redhat.com
Signed-off-by: Linus Torvalds

mm: swap: make page_evictable() inline

2020-04-02T16:35:27+00:00

When backporting commit 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping
pagevecs") to our 4.9 kernel, our test bench noticed around 10% down with
a couple of vm-scalability's test cases (lru-file-readonce,
lru-file-readtwice and lru-file-mmap-read). I didn't see that much down
on my VM (32c-64g-2nodes). It might be caused by the test configuration,
which is 32c-256g with NUMA disabled and the tests were run in root memcg,
so the tests actually stress only one inactive and active lru. It sounds
not very usual in mordern production environment.

That commit did two major changes:
1. Call page_evictable()
2. Use smp_mb to force the PG_lru set visible

It looks they contribute the most overhead. The page_evictable() is a
function which does function prologue and epilogue, and that was used by
page reclaim path only. However, lru add is a very hot path, so it sounds
better to make it inline. However, it calls page_mapping() which is not
inlined either, but the disassemble shows it doesn't do push and pop
operations and it sounds not very straightforward to inline it.

Other than this, it sounds smp_mb() is not necessary for x86 since
SetPageLRU is atomic which enforces memory barrier already, replace it
with smp_mb__after_atomic() in the following patch.

With the two fixes applied, the tests can get back around 5% on that test
bench and get back normal on my VM. Since the test bench configuration is
not that usual and I also saw around 6% up on the latest upstream, so it
sounds good enough IMHO.

The below is test data (lru-file-readtwice throughput) against the v5.6-rc4:
mainline w/ inline fix
150MB 154MB

With this patch the throughput gets 2.67% up. The data with using
smp_mb__after_atomic() is showed in the following patch.

Shakeel Butt did the below test:

On a real machine with limiting the 'dd' on a single node and reading 100
GiB sparse file (less than a single node). Just ran a single instance to
not cause the lru lock contention. The cmdline used is "dd if=file-100GiB
of=/dev/null bs=4k". Ran the cmd 10 times with drop_caches in between and
measured the time it took.

Without patch: 56.64143 +- 0.672 sec

With patches: 56.10 +- 0.21 sec

[akpm@linux-foundation.org: move page_evictable() to internal.h]
Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs")
Signed-off-by: Yang Shi
Signed-off-by: Andrew Morton
Tested-by: Shakeel Butt
Reviewed-by: Shakeel Butt
Reviewed-by: Matthew Wilcox (Oracle)
Acked-by: Vlastimil Babka
Acked-by: Johannes Weiner
Link: http://lkml.kernel.org/r/1584500541-46817-1-git-send-email-yang.shi@linux.alibaba.com
Signed-off-by: Linus Torvalds

mm, pcpu: make zone pcp updates and reset internal to the mm

2019-12-01T20:59:06+00:00

Memory hotplug needs to be able to reset and reinit the pcpu allocator
batch and high limits but this action is internal to the VM.  Move the
declaration to internal.h

Link: http://lkml.kernel.org/r/20191021094808.28824-4-mgorman@techsingularity.net
Signed-off-by: Mel Gorman 
Acked-by: Michal Hocko 
Acked-by: Vlastimil Babka 
Cc: Borislav Petkov 
Cc: Matt Fleming 
Cc: Qian Cai 
Cc: Thomas Gleixner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/mmap.c: rb_parent is not necessary in __vma_link_list()

2019-12-01T14:29:19+00:00

Now we use rb_parent to get next, while this is not necessary.

When prev is NULL, this means vma should be the first element in the list.
Then next should be current first one (mm->mmap), no matter whether we
have parent or not.

After removing it, the code shows the beauty of symmetry.

Link: http://lkml.kernel.org/r/20190813032656.16625-1-richardw.yang@linux.intel.com
Signed-off-by: Wei Yang 
Acked-by: Andrew Morton 
Cc: Mel Gorman 
Cc: Vlastimil Babka 
Cc: Matthew Wilcox 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/mmap.c: extract __vma_unlink_list() as counterpart for __vma_link_list()

2019-12-01T14:29:19+00:00

Just make the code a little easier to read.

Link: http://lkml.kernel.org/r/20191006012636.31521-3-richardw.yang@linux.intel.com
Signed-off-by: Wei Yang 
Cc: Christoph Hellwig 
Cc: Matthew Wilcox (Oracle) 
Cc: Mel Gorman 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: drop mmap_sem before calling balance_dirty_pages() in write fault

2019-12-01T14:29:18+00:00

One of our services is observing hanging ps/top/etc under heavy write
IO, and the task states show this is an mmap_sem priority inversion:

A write fault is holding the mmap_sem in read-mode and waiting for
(heavily cgroup-limited) IO in balance_dirty_pages():

    balance_dirty_pages+0x724/0x905
    balance_dirty_pages_ratelimited+0x254/0x390
    fault_dirty_shared_page.isra.96+0x4a/0x90
    do_wp_page+0x33e/0x400
    __handle_mm_fault+0x6f0/0xfa0
    handle_mm_fault+0xe4/0x200
    __do_page_fault+0x22b/0x4a0
    page_fault+0x45/0x50

Somebody tries to change the address space, contending for the mmap_sem in
write-mode:

    call_rwsem_down_write_failed_killable+0x13/0x20
    do_mprotect_pkey+0xa8/0x330
    SyS_mprotect+0xf/0x20
    do_syscall_64+0x5b/0x100
    entry_SYSCALL_64_after_hwframe+0x3d/0xa2

The waiting writer locks out all subsequent readers to avoid lock
starvation, and several threads can be seen hanging like this:

    call_rwsem_down_read_failed+0x14/0x30
    proc_pid_cmdline_read+0xa0/0x480
    __vfs_read+0x23/0x140
    vfs_read+0x87/0x130
    SyS_read+0x42/0x90
    do_syscall_64+0x5b/0x100
    entry_SYSCALL_64_after_hwframe+0x3d/0xa2

To fix this, do what we do for cache read faults already: drop the
mmap_sem before calling into anything IO bound, in this case the
balance_dirty_pages() function, and return VM_FAULT_RETRY.

Link: http://lkml.kernel.org/r/20190924194238.GA29030@cmpxchg.org
Signed-off-by: Johannes Weiner 
Reviewed-by: Matthew Wilcox (Oracle) 
Acked-by: Kirill A. Shutemov 
Cc: Josef Bacik 
Cc: Hillf Danton 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: introduce MADV_COLD

2019-09-26T00:51:41+00:00

Patch series "Introduce MADV_COLD and MADV_PAGEOUT", v7.

- Background

The Android terminology used for forking a new process and starting an app
from scratch is a cold start, while resuming an existing app is a hot
start.  While we continually try to improve the performance of cold
starts, hot starts will always be significantly less power hungry as well
as faster so we are trying to make hot start more likely than cold start.

To increase hot start, Android userspace manages the order that apps
should be killed in a process called ActivityManagerService.
ActivityManagerService tracks every Android app or service that the user
could be interacting with at any time and translates that into a ranked
list for lmkd(low memory killer daemon).  They are likely to be killed by
lmkd if the system has to reclaim memory.  In that sense they are similar
to entries in any other cache.  Those apps are kept alive for
opportunistic performance improvements but those performance improvements
will vary based on the memory requirements of individual workloads.

- Problem

Naturally, cached apps were dominant consumers of memory on the system.
However, they were not significant consumers of swap even though they are
good candidate for swap.  Under investigation, swapping out only begins
once the low zone watermark is hit and kswapd wakes up, but the overall
allocation rate in the system might trip lmkd thresholds and cause a
cached process to be killed(we measured performance swapping out vs.
zapping the memory by killing a process.  Unsurprisingly, zapping is 10x
times faster even though we use zram which is much faster than real
storage) so kill from lmkd will often satisfy the high zone watermark,
resulting in very few pages actually being moved to swap.

- Approach

The approach we chose was to use a new interface to allow userspace to
proactively reclaim entire processes by leveraging platform information.
This allowed us to bypass the inaccuracy of the kernel’s LRUs for pages
that are known to be cold from userspace and to avoid races with lmkd by
reclaiming apps as soon as they entered the cached state.  Additionally,
it could provide many chances for platform to use much information to
optimize memory efficiency.

To achieve the goal, the patchset introduce two new options for madvise.
One is MADV_COLD which will deactivate activated pages and the other is
MADV_PAGEOUT which will reclaim private pages instantly.  These new
options complement MADV_DONTNEED and MADV_FREE by adding non-destructive
ways to gain some free memory space.  MADV_PAGEOUT is similar to
MADV_DONTNEED in a way that it hints the kernel that memory region is not
currently needed and should be reclaimed immediately; MADV_COLD is similar
to MADV_FREE in a way that it hints the kernel that memory region is not
currently needed and should be reclaimed when memory pressure rises.

This patch (of 5):

When a process expects no accesses to a certain memory range, it could
give a hint to kernel that the pages can be reclaimed when memory pressure
happens but data should be preserved for future use.  This could reduce
workingset eviction so it ends up increasing performance.

This patch introduces the new MADV_COLD hint to madvise(2) syscall.
MADV_COLD can be used by a process to mark a memory range as not expected
to be used in the near future.  The hint can help kernel in deciding which
pages to evict early during memory pressure.

It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves

	active file page -> inactive file LRU
	active anon page -> inacdtive anon LRU

Unlike MADV_FREE, it doesn't move active anonymous pages to inactive file
LRU's head because MADV_COLD is a little bit different symantic.
MADV_FREE means it's okay to discard when the memory pressure because the
content of the page is *garbage* so freeing such pages is almost zero
overhead since we don't need to swap out and access afterward causes just
minor fault.  Thus, it would make sense to put those freeable pages in
inactive file LRU to compete other used-once pages.  It makes sense for
implmentaion point of view, too because it's not swapbacked memory any
longer until it would be re-dirtied.  Even, it could give a bonus to make
them be reclaimed on swapless system.  However, MADV_COLD doesn't mean
garbage so reclaiming them requires swap-out/in in the end so it's bigger
cost.  Since we have designed VM LRU aging based on cost-model, anonymous
cold pages would be better to position inactive anon's LRU list, not file
LRU.  Furthermore, it would help to avoid unnecessary scanning if system
doesn't have a swap device.  Let's start simpler way without adding
complexity at this moment.  However, keep in mind, too that it's a caveat
that workloads with a lot of pages cache are likely to ignore MADV_COLD on
anonymous memory because we rarely age anonymous LRU lists.

* man-page material

MADV_COLD (since Linux x.x)

Pages in the specified regions will be treated as less-recently-accessed
compared to pages in the system with similar access frequencies.  In
contrast to MADV_FREE, the contents of the region are preserved regardless
of subsequent writes to pages.

MADV_COLD cannot be applied to locked pages, Huge TLB pages, or VM_PFNMAP
pages.

[akpm@linux-foundation.org: resolve conflicts with hmm.git]
Link: http://lkml.kernel.org/r/20190726023435.214162-2-minchan@kernel.org
Signed-off-by: Minchan Kim 
Reported-by: kbuild test robot 
Acked-by: Michal Hocko 
Acked-by: Johannes Weiner 
Cc: James E.J. Bottomley 
Cc: Richard Henderson 
Cc: Ralf Baechle 
Cc: Chris Zankel 
Cc: Johannes Weiner 
Cc: Daniel Colascione 
Cc: Dave Hansen 
Cc: Hillf Danton 
Cc: Joel Fernandes (Google) 
Cc: Kirill A. Shutemov 
Cc: Oleksandr Natalenko 
Cc: Shakeel Butt 
Cc: Sonny Rao 
Cc: Suren Baghdasaryan 
Cc: Tim Murray 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds