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    Subject[PATCH 00/10] [v7][RESEND] Migrate Pages in lieu of discard
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    I'm resending this because I forgot to cc the mailing lists on the
    post yesterday. Sorry for the noise. Please reply to this series.

    The full series is also available here:

    https://github.com/hansendc/linux/tree/automigrate-20210331

    which also inclues some vm.zone_reclaim_mode sysctl ABI fixup
    prerequisites:

    https://github.com/hansendc/linux/commit/18daad8f0181a2da57cb43e595303c2ef5bd7b6e
    https://github.com/hansendc/linux/commit/a873f3b6f250581072ab36f2735a3aa341e36705

    There are no major changes since the last post.

    --

    We're starting to see systems with more and more kinds of memory such
    as Intel's implementation of persistent memory.

    Let's say you have a system with some DRAM and some persistent memory.
    Today, once DRAM fills up, reclaim will start and some of the DRAM
    contents will be thrown out. Allocations will, at some point, start
    falling over to the slower persistent memory.

    That has two nasty properties. First, the newer allocations can end
    up in the slower persistent memory. Second, reclaimed data in DRAM
    are just discarded even if there are gobs of space in persistent
    memory that could be used.

    This set implements a solution to these problems. At the end of the
    reclaim process in shrink_page_list() just before the last page
    refcount is dropped, the page is migrated to persistent memory instead
    of being dropped.

    While I've talked about a DRAM/PMEM pairing, this approach would
    function in any environment where memory tiers exist.

    This is not perfect. It "strands" pages in slower memory and never
    brings them back to fast DRAM. Huang Ying has follow-on work which
    repurposes autonuma to promote hot pages back to DRAM.

    This is also all based on an upstream mechanism that allows
    persistent memory to be onlined and used as if it were volatile:

    http://lkml.kernel.org/r/20190124231441.37A4A305@viggo.jf.intel.com

    == Open Issues ==

    * Memory policies and cpusets that, for instance, restrict allocations
    to DRAM can be demoted to PMEM whenever they opt in to this
    new mechanism. A cgroup-level API to opt-in or opt-out of
    these migrations will likely be required as a follow-on.
    * Could be more aggressive about where anon LRU scanning occurs
    since it no longer necessarily involves I/O. get_scan_count()
    for instance says: "If we have no swap space, do not bother
    scanning anon pages"

    --

    Documentation/admin-guide/sysctl/vm.rst | 12 +
    include/linux/migrate.h | 14 +-
    include/linux/swap.h | 3 +-
    include/linux/vm_event_item.h | 2 +
    include/trace/events/migrate.h | 3 +-
    include/uapi/linux/mempolicy.h | 1 +
    mm/compaction.c | 3 +-
    mm/gup.c | 3 +-
    mm/internal.h | 5 +
    mm/memory-failure.c | 4 +-
    mm/memory_hotplug.c | 4 +-
    mm/mempolicy.c | 8 +-
    mm/migrate.c | 315 +++++++++++++++++++++++-
    mm/page_alloc.c | 11 +-
    mm/vmscan.c | 158 +++++++++++-
    mm/vmstat.c | 2 +
    16 files changed, 520 insertions(+), 28 deletions(-)

    --

    Changes since (automigrate-20210304):
    * Add ack/review tags
    * Remove duplicate synchronize_rcu() call

    Changes since (automigrate-20210122):
    * move from GFP_HIGHUSER -> GFP_HIGHUSER_MOVABLE since pages *are*
    movable.
    * Separate out helpers that check for being able to relaim anonymous
    pages versus being able to meaningfully scan the anon LRU.

    Changes since (automigrate-20200818):
    * Fall back to normal reclaim when demotion fails
    * Fix some compile issues, when page migration and NUMA are off

    Changes since (automigrate-20201007):
    * separate out checks for "can scan anon LRU" from "can actually
    swap anon pages right now". Previous series conflated them
    and may have been overly aggressive scanning LRU
    * add MR_DEMOTION to tracepoint header
    * remove unnecessary hugetlb page check

    Changes since (https://lwn.net/Articles/824830/):
    * Use higher-level migrate_pages() API approach from Yang Shi's
    earlier patches.
    * made sure to actually check node_reclaim_mode's new bit
    * disabled migration entirely before introducing RECLAIM_MIGRATE
    * Replace GFP_NOWAIT with explicit __GFP_KSWAPD_RECLAIM and
    comment why we want that.
    * Comment on effects of that keep multiple source nodes from
    sharing target nodes

    Cc: Yang Shi <yang.shi@linux.alibaba.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Huang Ying <ying.huang@intel.com>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: David Hildenbrand <david@redhat.com>
    Cc: osalvador <osalvador@suse.de>
    Cc: Huang Ying <ying.huang@intel.com>
    Cc: Wei Xu <weixugc@google.com>

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