Not specifically tcp_collapse, but the article theorizes that some memory management done by tcp_collapse (i.e. GC) is the cause.  I&#x27;d place my bets on memory calls being the cause too.<p>But... they never went to the next step and confirmed that tcp_collapse was making lengthy system memory calls.  They kind of gloss over the details of why reducing rmem alleviates the problem.<p>Is it because with smaller rmem tcp_collapse aggregates segments into smaller sk_buffs, and these smaller-size memory calls don&#x27;t take as long to return?<p>Or is it because tcp_collapse has less memory &quot;stitching&quot; to do, since it can&#x27;t fit as many segments into the smaller sk_buffs?