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From: bugzilla@dpdk.org
To: dev@dpdk.org
Subject: [wishes/any Bug 1912] free mbufs should not have next and nb_segs
 initialized
Date: Wed, 25 Mar 2026 09:44:14 +0000
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http://bugs.dpdk.org/show_bug.cgi?id=3D1912

            Bug ID: 1912
           Summary: free mbufs should not have next and nb_segs
                    initialized
           Product: wishes
           Version: unspecified
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: any
          Assignee: dev@dpdk.org
          Reporter: mb@smartsharesystems.com
  Target Milestone: ---
             Group: wishes-managers

The invariant about which mbuf fields are initialized for free mbufs (i.e.
mbufs held in a mempool) should only cover the refcnt and the constant fiel=
ds:
buf_addr, buf_iova, buf_len, pool, priv_size.
The "next" and "nb_segs" fields are the only remaining non-constant fields =
(in
addition to the refcnt) still covered, and they should not be.

When an mbuf has been allocated and the driver fills the mbuf's fields duri=
ng
Rx, the driver might as well also set the "next" and "nb_segs" fields (if it
doesn't already).
The performance cost of setting these two fields along with the other field=
s is
near zero.

Not having to initialize any mbuf fields when freeing an mbuf would reduce =
the
performance cost of freeing mbufs.
And in the FAST_FREE case (where the refcnt is known to be 1), the driver c=
an
free the mbufs without touching them at all.

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