archive mirror
 help / color / mirror / Atom feed
From: Israel Rukshin <>
To: Linux-nvme <>,
	Sagi Grimberg <>, Christoph Hellwig <>,
	James Smart <>,
	Keith Busch <>
Cc: Israel Rukshin <>, Max Gurtovoy <>
Subject: [PATCH 0/3] nvme: Avoid preallocating big SGL for data
Date: Sun, 24 Nov 2019 18:38:29 +0200	[thread overview]
Message-ID: <> (raw)

When nvme allocates a tagset it preallocates a big buffer for the IO SGL
based on SG_CHUNK_SIZE.

Modern DMA engines are often capable of dealing with very big segments so
the SG_CHUNK_SIZE is often too big. SG_CHUNK_SIZE results in a static 4KB
SGL allocation per command.

If a controller has lots of deep queues, preallocation for the sg list can
consume substantial amounts of memory. Switch to runtime allocation for SGL
for lists longer than 2 entries. This is the approach used by NVMe PCI so
it should be reasonable for NVMeOF 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.

Israel Rukshin (3):
  nvme-rdma: Avoid preallocating big SGL for data
  nvme-fc: Avoid preallocating big SGL for data
  nvmet-loop: Avoid preallocating big SGL for data

 drivers/nvme/host/fc.c     |  8 ++++----
 drivers/nvme/host/nvme.h   |  6 ++++++
 drivers/nvme/host/rdma.c   | 10 +++++-----
 drivers/nvme/target/loop.c |  8 ++++----
 4 files changed, 19 insertions(+), 13 deletions(-)


Linux-nvme mailing list

             reply	other threads:[~2019-11-24 16:39 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-24 16:38 Israel Rukshin [this message]
2019-11-24 16:38 ` [PATCH 1/3] nvme-rdma: Avoid preallocating big SGL for data Israel Rukshin
2019-11-26 16:53   ` Christoph Hellwig
2019-11-24 16:38 ` [PATCH 2/3] nvme-fc: " Israel Rukshin
2019-11-25 17:04   ` James Smart
2019-11-24 16:38 ` [PATCH 3/3] nvmet-loop: " Israel Rukshin
2019-11-25  2:24   ` Chaitanya Kulkarni
2019-11-26 16:53   ` Christoph Hellwig
2019-11-26 17:40   ` Keith Busch

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).