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Bug#1111052: Please increase default UDP buffer size limits

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On Wed, 13 Aug 2025 20:11:36 -0700 Josh Triplett <josh@joshtriplett.org>
wrote:
> Package: linux-sysctl-defaults
> Version: 4.14
> Severity: wishlist
> File: /usr/lib/sysctl.d/50-default.conf
> X-Debbugs-Cc: josh@joshtriplett.org
> 
> Current uses of QUIC benefit from higher buffer size limits. Please
> consider setting:
> 
> net.core.rmem_max = 7500000

I can see that it makes sense to increase this to allow increasing the
receive window if the QUIC implementation sets its receive window based
on this, or otherwise to reduce the risk of packets being dropped if
user-space is slow to handle them.

I would like to see a detailed justification for the specific value,
though.

> net.core.wmem_max = 7500000

This seems wrong.  With QUIC the memory for replaying lost packets is
allocated in user-space, so I don't see any need to increase buffering
on the send side.  I think that this would mostly contribute to
bufferbloat.

> See https://github.com/quic-go/quic-go/wiki/UDP-Buffer-Sizes

No justification is given there for increasing wmem_max.

Ben.

-- 
Ben Hutchings
Time is nature's way of making sure that
everything doesn't happen at once.

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Thread

Bug#1111052: Please increase default UDP buffer size limits Josh Triplett <josh@joshtriplett.org> - 2025-08-14 05:20 +0200
  Processed: Re: Please increase default UDP buffer size limits "Debian Bug Tracking System" <owner@bugs.debian.org> - 2025-08-20 20:20 +0200
  Bug#1111052: Please increase default UDP buffer size limits Ben Hutchings <ben@decadent.org.uk> - 2025-08-20 20:20 +0200
  Bug#1111052: Backport upstream patch? Josh Triplett <josh@joshtriplett.org> - 2025-10-06 22:50 +0200
    Bug#1111657: Bug#1111052: Backport upstream patch? Salvatore Bonaccorso <carnil@debian.org> - 2025-10-13 08:40 +0200

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