• Minchan Kim's avatar
    zsmalloc: page migration support · 48b4800a
    Minchan Kim authored
    This patch introduces run-time migration feature for zspage.
    For migration, VM uses page.lru field so it would be better to not use
    page.next field which is unified with page.lru for own purpose.  For
    that, firstly, we can get first object offset of the page via runtime
    calculation instead of using page.index so we can use page.index as link
    for page chaining instead of page.next.
    In case of huge object, it stores handle to page.index instead of next
    link of page chaining because huge object doesn't need to next link for
    page chaining.  So get_next_page need to identify huge object to return
    NULL.  For it, this patch uses PG_owner_priv_1 flag of the page flag.
    For migration, it supports three functions
    * zs_page_isolate
    It isolates a zspage which includes a subpage VM want to migrate from
    class so anyone cannot allocate new object from the zspage.
    We could try to isolate a zspage by the number of subpage so subsequent
    isolation trial of other subpage of the zpsage shouldn't fail.  For
    that, we introduce zspage.isolated count.  With that, zs_page_isolate
    can know whether zspage is already isolated or not for migration so if
    it is isolated for migration, subsequent isolation trial can be
    successful without trying further isolation.
    * zs_page_migrate
    First of all, it holds write-side zspage->lock to prevent migrate other
    subpage in zspage.  Then, lock all objects in the page VM want to
    migrate.  The reason we should lock all objects in the page is due to
    race between zs_map_object and zs_page_migrate.
      zs_map_object				zs_page_migrate
      obj = handle_to_obj(handle)
      obj_to_location(obj, &page, &obj_idx);
    					if (!trypin_tag(handle))
    						goto unpin_object
      zspage = get_zspage(page);
    If zs_page_migrate doesn't do trypin_tag, zs_map_object's page can be
    stale by migration so it goes crash.
    If it locks all of objects successfully, it copies content from old page
    to new one, finally, create new zspage chain with new page.  And if it's
    last isolated subpage in the zspage, put the zspage back to class.
    * zs_page_putback
    It returns isolated zspage to right fullness_group list if it fails to
    migrate a page.  If it find a zspage is ZS_EMPTY, it queues zspage
    freeing to workqueue.  See below about async zspage freeing.
    This patch introduces asynchronous zspage free.  The reason to need it
    is we need page_lock to clear PG_movable but unfortunately, zs_free path
    should be atomic so the apporach is try to grab page_lock.  If it got
    page_lock of all of pages successfully, it can free zspage immediately.
    Otherwise, it queues free request and free zspage via workqueue in
    process context.
    If zs_free finds the zspage is isolated when it try to free zspage, it
    delays the freeing until zs_page_putback finds it so it will free free
    the zspage finally.
    In this patch, we expand fullness_list from ZS_EMPTY to ZS_FULL.  First
    of all, it will use ZS_EMPTY list for delay freeing.  And with adding
    ZS_FULL list, it makes to identify whether zspage is isolated or not via
    list_empty(&zspage->list) test.
    [minchan@kernel.org: zsmalloc: keep first object offset in struct page]
      Link: http://lkml.kernel.org/r/1465788015-23195-1-git-send-email-minchan@kernel.org
    [minchan@kernel.org: zsmalloc: zspage sanity check]
      Link: http://lkml.kernel.org/r/20160603010129.GC3304@bbox
    Link: http://lkml.kernel.org/r/1464736881-24886-12-git-send-email-minchan@kernel.orgSigned-off-by: default avatarMinchan Kim <minchan@kernel.org>
    Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
zsmalloc.c 60.4 KB