Date: Mon, 1 May 2017 06:03:44 +0000 (UTC) From: Alexander Motin <mav@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r317634 - stable/10/lib/libc/gen Message-ID: <201705010603.v4163iiD089496@repo.freebsd.org>
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Author: mav Date: Mon May 1 06:03:44 2017 New Revision: 317634 URL: https://svnweb.freebsd.org/changeset/base/317634 Log: MFC r317064: Optimize pathologic case of telldir() for Samba. When application reads large directory, calling telldir() for each entry, like Samba does, it creates exponential performance drop as number of entries reach tenths to hundreds of thousands. It is caused by full search through the internal list, that never finds matches in that scenario, but creates O(n^2) delays. This patch optimizes that search, limiting it to entries of the same buffer, turning time closer to O(n) in case of linear directory scan. Modified: stable/10/lib/libc/gen/telldir.c Directory Properties: stable/10/ (props changed) Modified: stable/10/lib/libc/gen/telldir.c ============================================================================== --- stable/10/lib/libc/gen/telldir.c Mon May 1 06:03:07 2017 (r317633) +++ stable/10/lib/libc/gen/telldir.c Mon May 1 06:03:44 2017 (r317634) @@ -53,15 +53,22 @@ long telldir(dirp) DIR *dirp; { - struct ddloc *lp; + struct ddloc *lp, *flp; long idx; if (__isthreaded) _pthread_mutex_lock(&dirp->dd_lock); + flp = NULL; LIST_FOREACH(lp, &dirp->dd_td->td_locq, loc_lqe) { - if (lp->loc_seek == dirp->dd_seek && - lp->loc_loc == dirp->dd_loc) + if (lp->loc_seek == dirp->dd_seek) { + if (flp == NULL) + flp = lp; + if (lp->loc_loc == dirp->dd_loc) + break; + } else if (flp != NULL) { + lp = NULL; break; + } } if (lp == NULL) { lp = malloc(sizeof(struct ddloc)); @@ -73,7 +80,10 @@ telldir(dirp) lp->loc_index = dirp->dd_td->td_loccnt++; lp->loc_seek = dirp->dd_seek; lp->loc_loc = dirp->dd_loc; - LIST_INSERT_HEAD(&dirp->dd_td->td_locq, lp, loc_lqe); + if (flp != NULL) + LIST_INSERT_BEFORE(flp, lp, loc_lqe); + else + LIST_INSERT_HEAD(&dirp->dd_td->td_locq, lp, loc_lqe); } idx = lp->loc_index; if (__isthreaded)
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