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Re: [Qemu-devel] [PATCH v3 2/5 for-3.0] qcow2: Options' documentation fi


From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v3 2/5 for-3.0] qcow2: Options' documentation fixes
Date: Tue, 24 Jul 2018 16:07:48 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 07/24/2018 03:03 PM, Leonid Bloch wrote:
Signed-off-by: Leonid Bloch <address@hidden>
---
  docs/qcow2-cache.txt |  3 +++
  qemu-options.hx      | 15 +++++++++++----
  2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/docs/qcow2-cache.txt b/docs/qcow2-cache.txt
index 8a09a5cc5f..9d261b7da9 100644
--- a/docs/qcow2-cache.txt
+++ b/docs/qcow2-cache.txt
@@ -130,6 +130,9 @@ There are a few things that need to be taken into account:
     memory as possible to the L2 cache before increasing the refcount
     cache size.
+- All three "l2-cache-size", "refcount-cache-size", and "cache-size" options
+  can not be set simultaneously.

Reads awkwardly; maybe:

At most two of "l2-cache-size", "refcount-cache-size", and "cache-size" can be set together on the command line (the omitted options are calculated accordingly).

+++ b/qemu-options.hx
@@ -752,15 +752,22 @@ image file)
@item cache-size
  The maximum total size of the L2 table and refcount block caches in bytes
-(default: 1048576 bytes or 8 clusters, whichever is larger)
@item l2-cache-size
-The maximum size of the L2 table cache in bytes
-(default: 4/5 of the total cache size)
+The maximum size of the L2 table cache.
+(default: if cache-size is not defined - 1048576 bytes or 8 clusters,
+whichever is larger; if cache-size is defined and is large enough to
+accommodate enough L2 cache to cover the entire virtual size of the image plus
+the minimal amount of refcount cache - enough to cover the entire image;
+if cache-size is defined and is not large enough - as much as possible while
+leaving space for the needed refcount cache)

Wordy; maybe:

(default: if cache-size is not defined - 1048576 bytes or 8 clusters, whichever is larger; otherwise, as large as possible within cache-size while still permitting the requested or minimum refcount cache size).

@item refcount-cache-size
  The maximum size of the refcount block cache in bytes
-(default: 1/5 of the total cache size)
+(default: 4 times the cluster size, or if cache-size is defined and is large
+enough to accommodate enough L2 cache to cover the entire virtual size of the
+image plus the minimal amount of refcount cache - the part of cache-size which
+is left after allocating the full L2 cache)

Maybe:

(default: 4 times the cluster size, plus any portion of a specified cache-size left over after sizing the L2 cache large enough to cover the entire image)

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org



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