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Date:      Sat, 29 Jun 2019 00:50:25 +0000 (UTC)
From:      John Baldwin <jhb@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r349531 - head/sys/kern
Message-ID:  <201906290050.x5T0oPJg033332@repo.freebsd.org>
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Author: jhb
Date: Sat Jun 29 00:50:25 2019
New Revision: 349531
URL: https://svnweb.freebsd.org/changeset/base/349531

Log:
  Compress pending socket buffer data once it is marked ready.
  
  Apply similar logic from sbcompress to pending data in the socket
  buffer once it is marked ready via sbready.  Normally sbcompress
  merges small mbufs to reduce the length of mbuf chains in the socket
  buffer.  However, sbcompress cannot do this for mbufs marked
  M_NOTREADY.  sbcompress_ready is now called from sbready when mbufs
  are marked ready to merge small mbuf chains once the data is available
  to copy.
  
  Submitted by:	gallatin (earlier version)
  Reviewed by:	gallatin, hselasky, rrs
  Sponsored by:	Netflix
  Differential Revision:	https://reviews.freebsd.org/D20616

Modified:
  head/sys/kern/uipc_sockbuf.c

Modified: head/sys/kern/uipc_sockbuf.c
==============================================================================
--- head/sys/kern/uipc_sockbuf.c	Sat Jun 29 00:49:35 2019	(r349530)
+++ head/sys/kern/uipc_sockbuf.c	Sat Jun 29 00:50:25 2019	(r349531)
@@ -89,6 +89,78 @@ sbm_clrprotoflags(struct mbuf *m, int flags)
 }
 
 /*
+ * Compress M_NOTREADY mbufs after they have been readied by sbready().
+ *
+ * sbcompress() skips M_NOTREADY mbufs since the data is not available to
+ * be copied at the time of sbcompress().  This function combines small
+ * mbufs similar to sbcompress() once mbufs are ready.  'm0' is the first
+ * mbuf sbready() marked ready, and 'end' is the first mbuf still not
+ * ready.
+ */
+static void
+sbready_compress(struct sockbuf *sb, struct mbuf *m0, struct mbuf *end)
+{
+	struct mbuf *m, *n;
+	int ext_size;
+
+	SOCKBUF_LOCK_ASSERT(sb);
+
+	if ((sb->sb_flags & SB_NOCOALESCE) != 0)
+		return;
+
+	for (m = m0; m != end; m = m->m_next) {
+		MPASS((m->m_flags & M_NOTREADY) == 0);
+
+		/* Compress small unmapped mbufs into plain mbufs. */
+		if ((m->m_flags & M_NOMAP) && m->m_len <= MLEN) {
+			MPASS(m->m_flags & M_EXT);
+			ext_size = m->m_ext.ext_size;
+			if (mb_unmapped_compress(m) == 0) {
+				sb->sb_mbcnt -= ext_size;
+				sb->sb_ccnt -= 1;
+			}
+		}
+
+		/*
+		 * NB: In sbcompress(), 'n' is the last mbuf in the
+		 * socket buffer and 'm' is the new mbuf being copied
+		 * into the trailing space of 'n'.  Here, the roles
+		 * are reversed and 'n' is the next mbuf after 'm'
+		 * that is being copied into the trailing space of
+		 * 'm'.
+		 */
+		n = m->m_next;
+		while ((n != NULL) && (n != end) && (m->m_flags & M_EOR) == 0 &&
+		    M_WRITABLE(m) &&
+		    (m->m_flags & M_NOMAP) == 0 &&
+		    n->m_len <= MCLBYTES / 4 && /* XXX: Don't copy too much */
+		    n->m_len <= M_TRAILINGSPACE(m) &&
+		    m->m_type == n->m_type) {
+			KASSERT(sb->sb_lastrecord != n,
+		    ("%s: merging start of record (%p) into previous mbuf (%p)",
+			    __func__, n, m));
+			m_copydata(n, 0, n->m_len, mtodo(m, m->m_len));
+			m->m_len += n->m_len;
+			m->m_next = n->m_next;
+			m->m_flags |= n->m_flags & M_EOR;
+			if (sb->sb_mbtail == n)
+				sb->sb_mbtail = m;
+
+			sb->sb_mbcnt -= MSIZE;
+			sb->sb_mcnt -= 1;
+			if (n->m_flags & M_EXT) {
+				sb->sb_mbcnt -= n->m_ext.ext_size;
+				sb->sb_ccnt -= 1;
+			}
+			m_free(n);
+			n = m->m_next;
+		}
+	}
+	SBLASTRECORDCHK(sb);
+	SBLASTMBUFCHK(sb);
+}
+
+/*
  * Mark ready "count" units of I/O starting with "m".  Most mbufs
  * count as a single unit of I/O except for EXT_PGS-backed mbufs which
  * can be backed by multiple pages.
@@ -138,6 +210,7 @@ sbready(struct sockbuf *sb, struct mbuf *m0, int count
 	}
 
 	if (!blocker) {
+		sbready_compress(sb, m0, m);
 		return (EINPROGRESS);
 	}
 
@@ -150,6 +223,7 @@ sbready(struct sockbuf *sb, struct mbuf *m0, int count
 	}
 
 	sb->sb_fnrdy = m;
+	sbready_compress(sb, m0, m);
 
 	return (0);
 }

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