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[Qemu-devel] [PULL 26/27] postcopy: Add doc about hugepages and postcopy
From: |
Dr. David Alan Gilbert (git) |
Subject: |
[Qemu-devel] [PULL 26/27] postcopy: Add doc about hugepages and postcopy |
Date: |
Tue, 28 Feb 2017 12:40:55 +0000 |
From: "Dr. David Alan Gilbert" <address@hidden>
Signed-off-by: Dr. David Alan Gilbert <address@hidden>
Reviewed-by: Juan Quintela <address@hidden>
Reviewed-by: Laurent Vivier <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Dr. David Alan Gilbert <address@hidden>
---
docs/migration.txt | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/docs/migration.txt b/docs/migration.txt
index c8b0304..1b940a8 100644
--- a/docs/migration.txt
+++ b/docs/migration.txt
@@ -540,3 +540,16 @@ request for a page that has already been sent is ignored.
Duplicate requests
such as this can happen as a page is sent at about the same time the
destination accesses it.
+=== Postcopy with hugepages ===
+
+Postcopy now works with hugetlbfs backed memory:
+ a) The linux kernel on the destination must support userfault on hugepages.
+ b) The huge-page configuration on the source and destination VMs must be
+ identical; i.e. RAMBlocks on both sides must use the same page size.
+ c) Note that -mem-path /dev/hugepages will fall back to allocating normal
+ RAM if it doesn't have enough hugepages, triggering (b) to fail.
+ Using -mem-prealloc enforces the allocation using hugepages.
+ d) Care should be taken with the size of hugepage used; postcopy with 2MB
+ hugepages works well, however 1GB hugepages are likely to be problematic
+ since it takes ~1 second to transfer a 1GB hugepage across a 10Gbps link,
+ and until the full page is transferred the destination thread is blocked.
--
2.9.3
- [Qemu-devel] [PULL 17/27] postcopy: Record largest page size, (continued)
- [Qemu-devel] [PULL 17/27] postcopy: Record largest page size, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 15/27] exec: ram_block_discard_range, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 18/27] postcopy: Plumb pagesize down into place helpers, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 19/27] postcopy: Use temporary for placing zero huge pages, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 20/27] postcopy: Load huge pages in one go, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 21/27] postcopy: Mask fault addresses to huge page boundary, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 22/27] postcopy: Send whole huge pages, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 23/27] postcopy: Allow hugepages, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 24/27] postcopy: Update userfaultfd.h header, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 25/27] postcopy: Check for userfault+hugepage feature, Dr. David Alan Gilbert (git), 2017/02/28
- [Qemu-devel] [PULL 26/27] postcopy: Add doc about hugepages and postcopy,
Dr. David Alan Gilbert (git) <=
- [Qemu-devel] [PULL 27/27] postcopy: Add extra check for COPY function, Dr. David Alan Gilbert (git), 2017/02/28