virito-mem: document Sub Block Mode (SBM)
Let's add some documentation for the current mode - Sub Block Mode (SBM) - to prepare for a new mode - Big Block Mode (BBM). Follow-up patches will properly factor out the existing Sub Block Mode (SBM) and implement Big Block Mode (BBM). Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com> Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Jason Wang <jasowang@redhat.com> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com> Signed-off-by: David Hildenbrand <david@redhat.com> Link: https://lore.kernel.org/r/20201112133815.13332-18-david@redhat.com Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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@ -27,6 +27,21 @@ static bool unplug_online = true;
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module_param(unplug_online, bool, 0644);
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MODULE_PARM_DESC(unplug_online, "Try to unplug online memory");
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/*
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* virtio-mem currently supports the following modes of operation:
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*
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* * Sub Block Mode (SBM): A Linux memory block spans 1..X subblocks (SB). The
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* size of a Sub Block (SB) is determined based on the device block size, the
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* pageblock size, and the maximum allocation granularity of the buddy.
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* Subblocks within a Linux memory block might either be plugged or unplugged.
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* Memory is added/removed to Linux MM in Linux memory block granularity.
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*
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* User space / core MM (auto onlining) is responsible for onlining added
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* Linux memory blocks - and for selecting a zone. Linux Memory Blocks are
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* always onlined separately, and all memory within a Linux memory block is
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* onlined to the same zone - virtio-mem relies on this behavior.
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*/
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enum virtio_mem_mb_state {
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/* Unplugged, not added to Linux. Can be reused later. */
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VIRTIO_MEM_MB_STATE_UNUSED = 0,
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