linux-toradex.git/include/linux/swap.h, branch v4.11-rc3

mm/swap: add cache for swap slots allocation

2017-02-23T00:41:30+00:00

We add per cpu caches for swap slots that can be allocated and freed
quickly without the need to touch the swap info lock.

Two separate caches are maintained for swap slots allocated and swap
slots returned.  This is to allow the swap slots to be returned to the
global pool in a batch so they will have a chance to be coaelesced with
other slots in a cluster.  We do not reuse the slots that are returned
right away, as it may increase fragmentation of the slots.

The swap allocation cache is protected by a mutex as we may sleep when
searching for empty slots in cache.  The swap free cache is protected by
a spin lock as we cannot sleep in the free path.

We refill the swap slots cache when we run out of slots, and we disable
the swap slots cache and drain the slots if the global number of slots
fall below a low watermark threshold.  We re-enable the cache agian when
the slots available are above a high watermark.

[ying.huang@intel.com: use raw_cpu_ptr over this_cpu_ptr for swap slots access]
[tim.c.chen@linux.intel.com: add comments on locks in swap_slots.h]
  Link: http://lkml.kernel.org/r/20170118180327.GA24225@linux.intel.com
Link: http://lkml.kernel.org/r/35de301a4eaa8daa2977de6e987f2c154385eb66.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen 
Signed-off-by: "Huang, Ying" 
Reviewed-by: Michal Hocko 
Cc: Aaron Lu 
Cc: Andi Kleen 
Cc: Andrea Arcangeli 
Cc: Christian Borntraeger 
Cc: Dave Hansen 
Cc: Hillf Danton 
Cc: Huang Ying 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Jonathan Corbet  escreveu:
Cc: Kirill A. Shutemov 
Cc: Minchan Kim 
Cc: Rik van Riel 
Cc: Shaohua Li 
Cc: Vladimir Davydov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/swap: free swap slots in batch

2017-02-23T00:41:30+00:00

Add new functions that free unused swap slots in batches without the
need to reacquire swap info lock.  This improves scalability and reduce
lock contention.

Link: http://lkml.kernel.org/r/c25e0fcdfd237ec4ca7db91631d3b9f6ed23824e.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen 
Signed-off-by: "Huang, Ying" 
Cc: Aaron Lu 
Cc: Andi Kleen 
Cc: Andrea Arcangeli 
Cc: Christian Borntraeger 
Cc: Dave Hansen 
Cc: Hillf Danton 
Cc: Huang Ying 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Jonathan Corbet  escreveu:
Cc: Kirill A. Shutemov 
Cc: Michal Hocko 
Cc: Minchan Kim 
Cc: Rik van Riel 
Cc: Shaohua Li 
Cc: Vladimir Davydov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/swap: allocate swap slots in batches

2017-02-23T00:41:30+00:00

Currently, the swap slots are allocated one page at a time, causing
contention to the swap_info lock protecting the swap partition on every
page being swapped.

This patch adds new functions get_swap_pages and scan_swap_map_slots to
request multiple swap slots at once.  This will reduces the lock
contention on the swap_info lock.  Also scan_swap_map_slots can operate
more efficiently as swap slots often occurs in clusters close to each
other on a swap device and it is quicker to allocate them together.

Link: http://lkml.kernel.org/r/9fec2845544371f62c3763d43510045e33d286a6.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen 
Signed-off-by: "Huang, Ying" 
Cc: Aaron Lu 
Cc: Andi Kleen 
Cc: Andrea Arcangeli 
Cc: Christian Borntraeger 
Cc: Dave Hansen 
Cc: Hillf Danton 
Cc: Huang Ying 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Jonathan Corbet  escreveu:
Cc: Kirill A. Shutemov 
Cc: Michal Hocko 
Cc: Minchan Kim 
Cc: Rik van Riel 
Cc: Shaohua Li 
Cc: Vladimir Davydov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/swap: skip readahead for unreferenced swap slots

2017-02-23T00:41:30+00:00

We can avoid needlessly allocating page for swap slots that are not used
by anyone.  No pages have to be read in for these slots.

Link: http://lkml.kernel.org/r/0784b3f20b9bd3aa5552219624cb78dc4ae710c9.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen 
Signed-off-by: "Huang, Ying" 
Cc: Aaron Lu 
Cc: Andi Kleen 
Cc: Andrea Arcangeli 
Cc: Christian Borntraeger 
Cc: Dave Hansen 
Cc: Hillf Danton 
Cc: Huang Ying 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Jonathan Corbet  escreveu:
Cc: Kirill A. Shutemov 
Cc: Michal Hocko 
Cc: Minchan Kim 
Cc: Rik van Riel 
Cc: Shaohua Li 
Cc: Vladimir Davydov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/swap: split swap cache into 64MB trunks

2017-02-23T00:41:30+00:00

The patch is to improve the scalability of the swap out/in via using
fine grained locks for the swap cache.  In current kernel, one address
space will be used for each swap device.  And in the common
configuration, the number of the swap device is very small (one is
typical).  This causes the heavy lock contention on the radix tree of
the address space if multiple tasks swap out/in concurrently.

But in fact, there is no dependency between pages in the swap cache.  So
that, we can split the one shared address space for each swap device
into several address spaces to reduce the lock contention.  In the
patch, the shared address space is split into 64MB trunks.  64MB is
chosen to balance the memory space usage and effect of lock contention
reduction.

The size of struct address_space on x86_64 architecture is 408B, so with
the patch, 6528B more memory will be used for every 1GB swap space on
x86_64 architecture.

One address space is still shared for the swap entries in the same 64M
trunks.  To avoid lock contention for the first round of swap space
allocation, the order of the swap clusters in the initial free clusters
list is changed.  The swap space distance between the consecutive swap
clusters in the free cluster list is at least 64M.  After the first
round of allocation, the swap clusters are expected to be freed
randomly, so the lock contention should be reduced effectively.

Link: http://lkml.kernel.org/r/735bab895e64c930581ffb0a05b661e01da82bc5.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: "Huang, Ying" 
Signed-off-by: Tim Chen 
Cc: Aaron Lu 
Cc: Andi Kleen 
Cc: Andrea Arcangeli 
Cc: Christian Borntraeger 
Cc: Dave Hansen 
Cc: Hillf Danton 
Cc: Huang Ying 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Jonathan Corbet  escreveu:
Cc: Kirill A. Shutemov 
Cc: Michal Hocko 
Cc: Minchan Kim 
Cc: Rik van Riel 
Cc: Shaohua Li 
Cc: Vladimir Davydov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/swap: add cluster lock

2017-02-23T00:41:30+00:00

This patch is to reduce the lock contention of swap_info_struct->lock
via using a more fine grained lock in swap_cluster_info for some swap
operations.  swap_info_struct->lock is heavily contended if multiple
processes reclaim pages simultaneously.  Because there is only one lock
for each swap device.  While in common configuration, there is only one
or several swap devices in the system.  The lock protects almost all
swap related operations.

In fact, many swap operations only access one element of
swap_info_struct->swap_map array.  And there is no dependency between
different elements of swap_info_struct->swap_map.  So a fine grained
lock can be used to allow parallel access to the different elements of
swap_info_struct->swap_map.

In this patch, a spinlock is added to swap_cluster_info to protect the
elements of swap_info_struct->swap_map in the swap cluster and the
fields of swap_cluster_info.  This reduced locking contention for
swap_info_struct->swap_map access greatly.

Because of the added spinlock, the size of swap_cluster_info increases
from 4 bytes to 8 bytes on the 64 bit and 32 bit system.  This will use
additional 4k RAM for every 1G swap space.

Because the size of swap_cluster_info is much smaller than the size of
the cache line (8 vs 64 on x86_64 architecture), there may be false
cache line sharing between spinlocks in swap_cluster_info.  To avoid the
false sharing in the first round of the swap cluster allocation, the
order of the swap clusters in the free clusters list is changed.  So
that, the swap_cluster_info sharing the same cache line will be placed
as far as possible.  After the first round of allocation, the order of
the clusters in free clusters list is expected to be random.  So the
false sharing should be not serious.

Compared with a previous implementation using bit_spin_lock, the
sequential swap out throughput improved about 3.2%.  Test was done on a
Xeon E5 v3 system.  The swap device used is a RAM simulated PMEM
(persistent memory) device.  To test the sequential swapping out, the
test case created 32 processes, which sequentially allocate and write to
the anonymous pages until the RAM and part of the swap device is used.

[ying.huang@intel.com: v5]
  Link: http://lkml.kernel.org/r/878tqeuuic.fsf_-_@yhuang-dev.intel.com
[minchan@kernel.org: initialize spinlock for swap_cluster_info]
  Link: http://lkml.kernel.org/r/1486434945-29753-1-git-send-email-minchan@kernel.org
[hughd@google.com: annotate nested locking for cluster lock]
  Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1702161050540.21773@eggly.anvils
Link: http://lkml.kernel.org/r/dbb860bbd825b1aaba18988015e8963f263c3f0d.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: "Huang, Ying" 
Signed-off-by: Tim Chen 
Signed-off-by: Minchan Kim 
Signed-off-by: Hugh Dickins 
Cc: Aaron Lu 
Cc: Andi Kleen 
Cc: Andrea Arcangeli 
Cc: Christian Borntraeger 
Cc: Dave Hansen 
Cc: Hillf Danton 
Cc: Huang Ying 
Cc: Hugh Dickins 
Cc: Johannes Weiner 
Cc: Jonathan Corbet  escreveu:
Cc: Kirill A. Shutemov 
Cc: Michal Hocko 
Cc: Minchan Kim 
Cc: Rik van Riel 
Cc: Shaohua Li 
Cc: Vladimir Davydov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: support anonymous stable page

2017-01-11T02:31:55+00:00

During developemnt for zram-swap asynchronous writeback, I found strange
corruption of compressed page, resulting in:

  Modules linked in: zram(E)
  CPU: 3 PID: 1520 Comm: zramd-1 Tainted: G            E   4.8.0-mm1-00320-ge0d4894c9c38-dirty #3274
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
  task: ffff88007620b840 task.stack: ffff880078090000
  RIP: set_freeobj.part.43+0x1c/0x1f
  RSP: 0018:ffff880078093ca8  EFLAGS: 00010246
  RAX: 0000000000000018 RBX: ffff880076798d88 RCX: ffffffff81c408c8
  RDX: 0000000000000018 RSI: 0000000000000000 RDI: 0000000000000246
  RBP: ffff880078093cb0 R08: 0000000000000000 R09: 0000000000000000
  R10: ffff88005bc43030 R11: 0000000000001df3 R12: ffff880076798d88
  R13: 000000000005bc43 R14: ffff88007819d1b8 R15: 0000000000000001
  FS:  0000000000000000(0000) GS:ffff88007e380000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007fc934048f20 CR3: 0000000077b01000 CR4: 00000000000406e0
  Call Trace:
    obj_malloc+0x22b/0x260
    zs_malloc+0x1e4/0x580
    zram_bvec_rw+0x4cd/0x830 [zram]
    page_requests_rw+0x9c/0x130 [zram]
    zram_thread+0xe6/0x173 [zram]
    kthread+0xca/0xe0
    ret_from_fork+0x25/0x30

With investigation, it reveals currently stable page doesn't support
anonymous page.  IOW, reuse_swap_page can reuse the page without waiting
writeback completion so it can overwrite page zram is compressing.

Unfortunately, zram has used per-cpu stream feature from v4.7.
It aims for increasing cache hit ratio of scratch buffer for
compressing. Downside of that approach is that zram should ask
memory space for compressed page in per-cpu context which requires
stricted gfp flag which could be failed. If so, it retries to
allocate memory space out of per-cpu context so it could get memory
this time and compress the data again, copies it to the memory space.

In this scenario, zram assumes the data should never be changed
but it is not true unless stable page supports. So, If the data is
changed under us, zram can make buffer overrun because second
compression size could be bigger than one we got in previous trial
and blindly, copy bigger size object to smaller buffer which is
buffer overrun. The overrun breaks zsmalloc free object chaining
so system goes crash like above.

I think below is same problem.
https://bugzilla.suse.com/show_bug.cgi?id=997574

Unfortunately, reuse_swap_page should be atomic so that we cannot wait on
writeback in there so the approach in this patch is simply return false if
we found it needs stable page.  Although it increases memory footprint
temporarily, it happens rarely and it should be reclaimed easily althoug
it happened.  Also, It would be better than waiting of IO completion,
which is critial path for application latency.

Fixes: da9556a2367c ("zram: user per-cpu compression streams")
Link: http://lkml.kernel.org/r/20161120233015.GA14113@bbox
Link: http://lkml.kernel.org/r/1482366980-3782-2-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim 
Acked-by: Hugh Dickins 
Cc: Sergey Senozhatsky 
Cc: Darrick J. Wong 
Cc: Takashi Iwai 
Cc: Hyeoncheol Lee 
Cc: 
Cc: Sangseok Lee 
Cc:  [4.7+]
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge branch 'for-4.10/block' of git://git.kernel.dk/linux-block

2016-12-13T18:19:16+00:00

Pull block layer updates from Jens Axboe:
 "This is the main block pull request this series. Contrary to previous
  release, I've kept the core and driver changes in the same branch. We
  always ended up having dependencies between the two for obvious
  reasons, so makes more sense to keep them together. That said, I'll
  probably try and keep more topical branches going forward, especially
  for cycles that end up being as busy as this one.

  The major parts of this pull request is:

   - Improved support for O_DIRECT on block devices, with a small
     private implementation instead of using the pig that is
     fs/direct-io.c. From Christoph.

   - Request completion tracking in a scalable fashion. This is utilized
     by two components in this pull, the new hybrid polling and the
     writeback queue throttling code.

   - Improved support for polling with O_DIRECT, adding a hybrid mode
     that combines pure polling with an initial sleep. From me.

   - Support for automatic throttling of writeback queues on the block
     side. This uses feedback from the device completion latencies to
     scale the queue on the block side up or down. From me.

   - Support from SMR drives in the block layer and for SD. From Hannes
     and Shaun.

   - Multi-connection support for nbd. From Josef.

   - Cleanup of request and bio flags, so we have a clear split between
     which are bio (or rq) private, and which ones are shared. From
     Christoph.

   - A set of patches from Bart, that improve how we handle queue
     stopping and starting in blk-mq.

   - Support for WRITE_ZEROES from Chaitanya.

   - Lightnvm updates from Javier/Matias.

   - Supoort for FC for the nvme-over-fabrics code. From James Smart.

   - A bunch of fixes from a whole slew of people, too many to name
     here"

* 'for-4.10/block' of git://git.kernel.dk/linux-block: (182 commits)
  blk-stat: fix a few cases of missing batch flushing
  blk-flush: run the queue when inserting blk-mq flush
  elevator: make the rqhash helpers exported
  blk-mq: abstract out blk_mq_dispatch_rq_list() helper
  blk-mq: add blk_mq_start_stopped_hw_queue()
  block: improve handling of the magic discard payload
  blk-wbt: don't throttle discard or write zeroes
  nbd: use dev_err_ratelimited in io path
  nbd: reset the setup task for NBD_CLEAR_SOCK
  nvme-fabrics: Add FC LLDD loopback driver to test FC-NVME
  nvme-fabrics: Add target support for FC transport
  nvme-fabrics: Add host support for FC transport
  nvme-fabrics: Add FC transport LLDD api definitions
  nvme-fabrics: Add FC transport FC-NVME definitions
  nvme-fabrics: Add FC transport error codes to nvme.h
  Add type 0x28 NVME type code to scsi fc headers
  nvme-fabrics: patch target code in prep for FC transport support
  nvme-fabrics: set sqe.command_id in core not transports
  parser: add u64 number parser
  nvme-rdma: align to generic ib_event logging helper
  ...

mm: workingset: move shadow entry tracking to radix tree exceptional tracking

2016-12-13T02:55:08+00:00

Currently, we track the shadow entries in the page cache in the upper
bits of the radix_tree_node->count, behind the back of the radix tree
implementation.  Because the radix tree code has no awareness of them,
we rely on random subtleties throughout the implementation (such as the
node->count != 1 check in the shrinking code, which is meant to exclude
multi-entry nodes but also happens to skip nodes with only one shadow
entry, as that's accounted in the upper bits).  This is error prone and
has, in fact, caused the bug fixed in d3798ae8c6f3 ("mm: filemap: don't
plant shadow entries without radix tree node").

To remove these subtleties, this patch moves shadow entry tracking from
the upper bits of node->count to the existing counter for exceptional
entries.  node->count goes back to being a simple counter of valid
entries in the tree node and can be shrunk to a single byte.

This vastly simplifies the page cache code.  All accounting happens
natively inside the radix tree implementation, and maintaining the LRU
linkage of shadow nodes is consolidated into a single function in the
workingset code that is called for leaf nodes affected by a change in
the page cache tree.

This also removes the last user of the __radix_delete_node() return
value.  Eliminate it.

Link: http://lkml.kernel.org/r/20161117193211.GE23430@cmpxchg.org
Signed-off-by: Johannes Weiner 
Reviewed-by: Jan Kara 
Cc: Kirill A. Shutemov 
Cc: Hugh Dickins 
Cc: Matthew Wilcox 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: only include blk_types in swap.h if CONFIG_SWAP is enabled

2016-11-01T15:43:26+00:00

It's only needed for the CONFIG_SWAP-only use of bio_end_io_t.

Because CONFIG_SWAP implies CONFIG_BLOCK this will allow to drop some
ifdefs in blk_types.h.

Instead we'll need to add a few explicit includes that were implicit
before, though.

Signed-off-by: Christoph Hellwig 
Signed-off-by: Jens Axboe