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From fac45a82432d342bf8cf86fab57af88ba54fb0f4 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Tue, 19 Feb 2019 17:00:19 +0100
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Subject: [PATCH 18/23] qcow2: Increase the default upper limit on the L2 cache
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size
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20190219170023.27826-10-kwolf@redhat.com>
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Patchwork-id: 84549
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O-Subject: [RHEL-7.7 qemu-kvm-rhev PATCH 09/13] qcow2: Increase the default upper limit on the L2 cache size
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Bugzilla: 1656913
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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From: Leonid Bloch <lbloch@janustech.com>
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The upper limit on the L2 cache size is increased from 1 MB to 32 MB
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on Linux platforms, and to 8 MB on other platforms (this difference is
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caused by the ability to set intervals for cache cleaning on Linux
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platforms only).
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This is done in order to allow default full coverage with the L2 cache
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for images of up to 256 GB in size (was 8 GB). Note, that only the
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needed amount to cover the full image is allocated. The value which is
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changed here is just the upper limit on the L2 cache size, beyond which
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it will not grow, even if the size of the image will require it to.
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Signed-off-by: Leonid Bloch <lbloch@janustech.com>
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Reviewed-by: Alberto Garcia <berto@igalia.com>
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Reviewed-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit 80668d0fb735f0839a46278a7d42116089b82816)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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block/qcow2.h | 6 +++++-
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docs/qcow2-cache.txt | 15 +++++++++------
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qemu-options.hx | 6 +++---
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3 files changed, 17 insertions(+), 10 deletions(-)
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diff --git a/block/qcow2.h b/block/qcow2.h
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index d0dd4a2..6c6c742 100644
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--- a/block/qcow2.h
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+++ b/block/qcow2.h
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@@ -74,7 +74,11 @@
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/* Must be at least 4 to cover all cases of refcount table growth */
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#define MIN_REFCOUNT_CACHE_SIZE 4 /* clusters */
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-#define DEFAULT_L2_CACHE_MAX_SIZE S_1MiB
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+#ifdef CONFIG_LINUX
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+#define DEFAULT_L2_CACHE_MAX_SIZE S_32MiB
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+#else
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+#define DEFAULT_L2_CACHE_MAX_SIZE S_8MiB
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+#endif
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#define DEFAULT_CLUSTER_SIZE S_64KiB
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diff --git a/docs/qcow2-cache.txt b/docs/qcow2-cache.txt
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index 750447e..1fcc065 100644
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--- a/docs/qcow2-cache.txt
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+++ b/docs/qcow2-cache.txt
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@@ -125,12 +125,15 @@ There are a few things that need to be taken into account:
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- Both caches must have a size that is a multiple of the cluster size
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(or the cache entry size: see "Using smaller cache sizes" below).
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- - The maximum L2 cache size is 1 MB by default (enough for full coverage
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- of 8 GB images, with the default cluster size). This value can be
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- modified using the "l2-cache-size" option. QEMU will not use more memory
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- than needed to hold all of the image's L2 tables, regardless of this max.
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- value. The minimal L2 cache size is 2 clusters (or 2 cache entries, see
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- below).
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+ - The maximum L2 cache size is 32 MB by default on Linux platforms (enough
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+ for full coverage of 256 GB images, with the default cluster size). This
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+ value can be modified using the "l2-cache-size" option. QEMU will not use
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+ more memory than needed to hold all of the image's L2 tables, regardless
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+ of this max. value.
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+ On non-Linux platforms the maximal value is smaller by default (8 MB) and
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+ this difference stems from the fact that on Linux the cache can be cleared
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+ periodically if needed, using the "cache-clean-interval" option (see below).
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+ The minimal L2 cache size is 2 clusters (or 2 cache entries, see below).
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- The default (and minimum) refcount cache size is 4 clusters.
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diff --git a/qemu-options.hx b/qemu-options.hx
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index e1fbc5b..3580d16 100644
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--- a/qemu-options.hx
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+++ b/qemu-options.hx
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@@ -756,9 +756,9 @@ The maximum total size of the L2 table and refcount block caches in bytes
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@item l2-cache-size
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The maximum size of the L2 table cache in bytes
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-(default: if cache-size is not specified - 1M; otherwise, as large as possible
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-within the cache-size, while permitting the requested or the minimal refcount
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-cache size)
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+(default: if cache-size is not specified - 32M on Linux platforms, and 8M on
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+non-Linux platforms; otherwise, as large as possible within the cache-size,
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+while permitting the requested or the minimal refcount cache size)
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@item refcount-cache-size
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The maximum size of the refcount block cache in bytes
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--
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1.8.3.1
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