From: NeilBrown <neilb@suse.de>
To: "J. Bruce Fields" <bfields@fieldses.org>,
"J. Bruce Fields" <bfields@redhat.com>
Cc: linux-nfs@vger.kernel.org
Subject: [PATCH - 2/2] nfsd: degraded slot-count more gracefully as allocation nears exhaustion.
Date: Fri, 20 Sep 2019 16:36:45 +1000 [thread overview]
Message-ID: <87zhiz8oea.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <8736gra34j.fsf@notabene.neil.brown.name>
[-- Attachment #1: Type: text/plain, Size: 3426 bytes --]
This original code in nfsd4_get_drc_mem() would hand out 30
slots (approximately NFSD_MAX_MEM_PER_SESSION bytes at slightly
over 2K per slot) to each requesting client until it ran out
of space, then it would possibly give one last client a reduced
allocation, then fail the allocation.
Since commit de766e570413 ("nfsd: give out fewer session slots as
limit approaches") the last 90 slots to be given to about 12
clients with quickly reducing slot counts (better than just 3
clients). This still seems unnecessarily hasty.
A subsequent patch allows over-allocation so every client gets
at least one slot, but that might be a bit restrictive.
The requested number of nfsd threads is the best guide we have to the
expected number of clients, so use that - if it is at least 8.
256 threads on a 256Meg machine - which is a lot for a tiny machine -
would result in nfsd_drc_max_mem being 2Meg, so 8K (3 slots) would be
available for the first client, and over 200 clients would get more
than 1 slot. So I don't think this change will be too debilitating on
poorly configured machines, though it does mean that a sensible
configuration is a little more important.
Signed-off-by: NeilBrown <neilb@suse.de>
---
fs/nfsd/nfs4state.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 084a30d77359..c49af2ba3924 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1563,11 +1563,12 @@ static inline u32 slot_bytes(struct nfsd4_channel_attrs *ca)
* re-negotiate active sessions and reduce their slot usage to make
* room for new connections. For now we just fail the create session.
*/
-static u32 nfsd4_get_drc_mem(struct nfsd4_channel_attrs *ca)
+static u32 nfsd4_get_drc_mem(struct nfsd4_channel_attrs *ca, struct nfsd_net *nn)
{
u32 slotsize = slot_bytes(ca);
u32 num = ca->maxreqs;
unsigned long avail, total_avail;
+ unsigned int scale_factor;
spin_lock(&nfsd_drc_lock);
if (nfsd_drc_max_mem > nfsd_drc_mem_used)
@@ -1581,12 +1582,18 @@ static u32 nfsd4_get_drc_mem(struct nfsd4_channel_attrs *ca)
total_avail = 0;
avail = min((unsigned long)NFSD_MAX_MEM_PER_SESSION, total_avail);
/*
- * Never use more than a third of the remaining memory,
+ * Never use more than a fraction of the remaining memory,
* unless it's the only way to give this client a slot.
+ * The chosen fraction is either 1/8 or 1/number of threads,
+ * whichever is smaller. This ensures there are adequate
+ * slots to support multiple clients per thread.
* Give the client one slot even that would require
* over-allocation, it is better than failure.
*/
- avail = clamp_t(unsigned long, avail, slotsize, total_avail/3);
+ scale_factor = max_t(unsigned int, 8, nn->nfsd_serv->sv_nrthreads);
+
+ avail = clamp_t(unsigned long, avail, slotsize,
+ total_avail/scale_factor);
num = min_t(int, num, avail / slotsize);
num = max_t(int, num, 1);
nfsd_drc_mem_used += num * slotsize;
@@ -3183,7 +3190,7 @@ static __be32 check_forechannel_attrs(struct nfsd4_channel_attrs *ca, struct nfs
* Note that we always allow at least one slot, because our
* accounting is soft and provides no guarantees either way.
*/
- ca->maxreqs = nfsd4_get_drc_mem(ca);
+ ca->maxreqs = nfsd4_get_drc_mem(ca, nn);
return nfs_ok;
}
--
2.23.0
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]
next prev parent reply other threads:[~2019-09-20 6:36 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-25 13:21 [PATCH 0/2] tweak knfsd session slot table sizing J. Bruce Fields
2017-09-25 13:21 ` [PATCH 1/2] nfsd: increase DRC cache limit J. Bruce Fields
2017-09-25 13:21 ` [PATCH 2/2] nfsd: give out fewer session slots as limit approaches J. Bruce Fields
2019-09-19 1:08 ` NeilBrown
2019-09-19 16:22 ` J. Bruce Fields
2019-09-19 17:17 ` J. Bruce Fields
2019-09-19 18:41 ` J. Bruce Fields
2019-09-20 6:15 ` [PATCH 1/2] nfsd: handle drc over-allocation gracefully NeilBrown
2019-09-20 6:33 ` [PATCH 1/2 - vers2] " NeilBrown
2019-09-20 6:36 ` NeilBrown [this message]
2019-09-20 16:28 ` J. Bruce Fields
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:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87zhiz8oea.fsf@notabene.neil.brown.name \
--to=neilb@suse.de \
--cc=bfields@fieldses.org \
--cc=bfields@redhat.com \
--cc=linux-nfs@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* 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).