Messages in this thread | | | Subject | Regression caused by commit c54f24e3 (nfsd: fix performance-limiting session calculation) | From | Paul Menzel <> | Date | Tue, 2 Jul 2019 23:59:48 +0200 |
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Dear Bruce,
Could it be that commit c54f24e3 (nfsd: fix performance-limiting session calculation) causes a regression on big memory machines (1 TB)?
> From c54f24e338ed2a35218f117a4a1afb5f9e2b4e64 Mon Sep 17 00:00:00 2001 > From: "J. Bruce Fields" <bfields@redhat.com> > Date: Thu, 21 Feb 2019 10:47:00 -0500 > Subject: [PATCH] nfsd: fix performance-limiting session calculation > > We're unintentionally limiting the number of slots per nfsv4.1 session > to 10. Often more than 10 simultaneous RPCs are needed for the best > performance. > > This calculation was meant to prevent any one client from using up more > than a third of the limit we set for total memory use across all clients > and sessions. Instead, it's limiting the client to a third of the > maximum for a single session. > > Fix this. > > Reported-by: Chris Tracy <ctracy@engr.scu.edu> > Cc: stable@vger.kernel.org > Fixes: de766e570413 "nfsd: give out fewer session slots as limit approaches" > Signed-off-by: J. Bruce Fields <bfields@redhat.com> > --- > fs/nfsd/nfs4state.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > index fb3c9844c82a..6a45fb00c5fc 100644 > --- a/fs/nfsd/nfs4state.c > +++ b/fs/nfsd/nfs4state.c > @@ -1544,16 +1544,16 @@ static u32 nfsd4_get_drc_mem(struct nfsd4_channel_attrs *ca) > { > u32 slotsize = slot_bytes(ca); > u32 num = ca->maxreqs; > - int avail; > + unsigned long avail, total_avail; > > spin_lock(&nfsd_drc_lock); > - avail = min((unsigned long)NFSD_MAX_MEM_PER_SESSION, > - nfsd_drc_max_mem - nfsd_drc_mem_used); > + total_avail = nfsd_drc_max_mem - nfsd_drc_mem_used; > + avail = min((unsigned long)NFSD_MAX_MEM_PER_SESSION, total_avail); > /* > * Never use more than a third of the remaining memory, > * unless it's the only way to give this client a slot: > */ > - avail = clamp_t(int, avail, slotsize, avail/3); > + avail = clamp_t(int, avail, slotsize, total_avail/3); > num = min_t(int, num, avail / slotsize); > nfsd_drc_mem_used += num * slotsize; > spin_unlock(&nfsd_drc_lock);
Booting a 80 threads, 1 TB server with Linux 4.19.56 and Linux 5.2-rc7 causes connections problems for the clients. The problems do not happen on servers with just 96 GB memory for example. Bisecting points to the two commits below (and I can only continue tomorrow).
c54f24e338ed2a35218f117a4a1afb5f9e2b4e64 (nfsd: fix performance-limiting session calculation) 8127d82705998568b52ac724e28e00941538083d (NFS: Don't recoalesce on error in nfs_pageio_complete_mirror())
If you have things I could do to verify this besides reverting it tomorrow, please tell. It’d be great if it could be fixed before Linux 5.2 is released.
Kind regards,
Paul
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