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[Qemu-devel] [PATCH v2 16/16] postcopy: Add doc about hugepages and post
From: |
Dr. David Alan Gilbert (git) |
Subject: |
[Qemu-devel] [PATCH v2 16/16] postcopy: Add doc about hugepages and postcopy |
Date: |
Mon, 6 Feb 2017 17:33:06 +0000 |
From: "Dr. David Alan Gilbert" <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 6503c17..b462ead 100644
--- a/docs/migration.txt
+++ b/docs/migration.txt
@@ -482,3 +482,16 @@ 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] [PATCH v2 08/16] postcopy: Plumb pagesize down into place helpers, (continued)
- [Qemu-devel] [PATCH v2 08/16] postcopy: Plumb pagesize down into place helpers, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 13/16] postcopy: Allow hugepages, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 14/16] postcopy: Update userfaultfd.h header, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 12/16] postcopy: Send whole huge pages, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 16/16] postcopy: Add doc about hugepages and postcopy,
Dr. David Alan Gilbert (git) <=
- [Qemu-devel] [PATCH v2 10/16] postcopy: Load huge pages in one go, Dr. David Alan Gilbert (git), 2017/02/06
- [Qemu-devel] [PATCH v2 15/16] postcopy: Check for userfault+hugepage feature, Dr. David Alan Gilbert (git), 2017/02/06
- Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support, Dr. David Alan Gilbert, 2017/02/06