5c82c94b0b
[ Upstream commit 02746e26c39ee473b975e0f68d1295abc92672ed ] No need to pre-allocate a big buffer for the IO SGL anymore. If a device has lots of deep queues, preallocation for the sg list can consume substantial amounts of memory. For HW virtio-blk device, nr_hw_queues can be 64 or 128 and each queue's depth might be 128. This means the resulting preallocation for the data SGLs is big. Switch to runtime allocation for SGL for lists longer than 2 entries. This is the approach used by NVMe drivers so it should be reasonable for virtio block as well. Runtime SGL allocation has always been the case for the legacy I/O path so this is nothing new. The preallocated small SGL depends on SG_CHAIN so if the ARCH doesn't support SG_CHAIN, use only runtime allocation for the SGL. Re-organize the setup of the IO request to fit the new sg chain mechanism. No performance degradation was seen (fio libaio engine with 16 jobs and 128 iodepth): IO size IOPs Rand Read (before/after) IOPs Rand Write (before/after) -------- --------------------------------- ---------------------------------- 512B 318K/316K 329K/325K 4KB 323K/321K 353K/349K 16KB 199K/208K 250K/275K 128KB 36K/36.1K 39.2K/41.7K Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com> Reviewed-by: Israel Rukshin <israelr@nvidia.com> Link: https://lore.kernel.org/r/20210901131434.31158-1-mgurtovoy@nvidia.com Reviewed-by: Feng Li <lifeng1519@gmail.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Tested-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Arnd Bergmann <arnd@arndb.de> # kconfig fixups Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.