From: Wei Liu <wei.liu@kernel.org>
To: mhklinux@outlook.com
Cc: haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com,
boqun.feng@gmail.com, linux-kernel@vger.kernel.org,
linux-hyperv@vger.kernel.org
Subject: Re: [PATCH v2 1/1] Drivers: hv: vmbus: Calculate ring buffer size for more efficient use of memory
Date: Fri, 1 Mar 2024 09:25:12 +0000 [thread overview]
Message-ID: <ZeGe-C9SYUYXPa_7@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <20240229004533.313662-1-mhklinux@outlook.com>
On Wed, Feb 28, 2024 at 04:45:33PM -0800, mhkelley58@gmail.com wrote:
> From: Michael Kelley <mhklinux@outlook.com>
>
> The VMBUS_RING_SIZE macro adds space for a ring buffer header to the
> requested ring buffer size. The header size is always 1 page, and so
> its size varies based on the PAGE_SIZE for which the kernel is built.
> If the requested ring buffer size is a large power-of-2 size and the header
> size is small, the resulting size is inefficient in its use of memory.
> For example, a 512 Kbyte ring buffer with a 4 Kbyte page size results in
> a 516 Kbyte allocation, which is rounded to up 1 Mbyte by the memory
> allocator, and wastes 508 Kbytes of memory.
>
> In such situations, the exact size of the ring buffer isn't that important,
> and it's OK to allocate the 4 Kbyte header at the beginning of the 512
> Kbytes, leaving the ring buffer itself with just 508 Kbytes. The memory
> allocation can be 512 Kbytes instead of 1 Mbyte and nothing is wasted.
>
> Update VMBUS_RING_SIZE to implement this approach for "large" ring buffer
> sizes. "Large" is somewhat arbitrarily defined as 8 times the size of
> the ring buffer header (which is of size PAGE_SIZE). For example, for
> 4 Kbyte PAGE_SIZE, ring buffers of 32 Kbytes and larger use the first
> 4 Kbytes as the ring buffer header. For 64 Kbyte PAGE_SIZE, ring buffers
> of 512 Kbytes and larger use the first 64 Kbytes as the ring buffer
> header. In both cases, smaller sizes add space for the header so
> the ring size isn't reduced too much by using part of the space for
> the header. For example, with a 64 Kbyte page size, we don't want
> a 128 Kbyte ring buffer to be reduced to 64 Kbytes by allocating half
> of the space for the header. In such a case, the memory allocation
> is less efficient, but it's the best that can be done.
>
> While the new algorithm slightly changes the amount of space allocated
> for ring buffers by drivers that use VMBUS_RING_SIZE, the devices aren't
> known to be sensitive to small changes in ring buffer size, so there
> shouldn't be any effect.
>
> Fixes: c1135c7fd0e9 ("Drivers: hv: vmbus: Introduce types of GPADL")
> Fixes: 6941f67ad37d ("hv_netvsc: Calculate correct ring size when PAGE_SIZE is not 4 Kbytes")
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218502
> Cc: stable@vger.kernel.org
> Signed-off-by: Michael Kelley <mhklinux@outlook.com>
> Reviewed-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> Reviewed-by: Dexuan Cui <decui@microsoft.com>
> Tested-by: Souradeep Chakrabarti <schakrabarti@linux.microsoft.com>
Applied to hyperv-fixes, thanks!
prev parent reply other threads:[~2024-03-01 9:25 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-29 0:45 [PATCH v2 1/1] Drivers: hv: vmbus: Calculate ring buffer size for more efficient use of memory mhkelley58
2024-03-01 9:25 ` Wei Liu [this message]
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