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Date:      Fri, 23 Oct 2020 15:49:18 +0000 (UTC)
From:      Mateusz Guzik <mjg@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r366974 - head/sys/kern
Message-ID:  <202010231549.09NFnIg4073710@repo.freebsd.org>
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Author: mjg
Date: Fri Oct 23 15:49:18 2020
New Revision: 366974
URL: https://svnweb.freebsd.org/changeset/base/366974

Log:
  vfs: stop taking the interlock in vnode reclaim
  
  It no longer protects any of tested fields, keeping all the checks racy.
  
  While here make vtryrecycle drop the vnode on its own. Avoids an additional
  lock trip.

Modified:
  head/sys/kern/vfs_subr.c

Modified: head/sys/kern/vfs_subr.c
==============================================================================
--- head/sys/kern/vfs_subr.c	Fri Oct 23 15:12:06 2020	(r366973)
+++ head/sys/kern/vfs_subr.c	Fri Oct 23 15:49:18 2020	(r366974)
@@ -1121,24 +1121,12 @@ restart:
 		if (vp->v_type == VBAD || vp->v_type == VNON)
 			goto next_iter;
 
-		if (!VI_TRYLOCK(vp))
-			goto next_iter;
-
-		if (vp->v_usecount > 0 || vp->v_holdcnt == 0 ||
-		    (!reclaim_nc_src && !LIST_EMPTY(&vp->v_cache_src)) ||
-		    VN_IS_DOOMED(vp) || vp->v_type == VNON) {
-			VI_UNLOCK(vp);
-			goto next_iter;
-		}
-
 		object = atomic_load_ptr(&vp->v_object);
 		if (object == NULL || object->resident_page_count > trigger) {
-			VI_UNLOCK(vp);
 			goto next_iter;
 		}
 
-		vholdl(vp);
-		VI_UNLOCK(vp);
+		vhold(vp);
 		TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
 		TAILQ_INSERT_AFTER(&vnode_list, vp, mvp, v_vnodelist);
 		mtx_unlock(&vnode_list_mtx);
@@ -1235,21 +1223,18 @@ restart:
 		 * blocking.
 		 */
 		if (vp->v_holdcnt > 0 || (mnt_op != NULL && (mp = vp->v_mount) != NULL &&
-		    mp->mnt_op != mnt_op) || !VI_TRYLOCK(vp)) {
+		    mp->mnt_op != mnt_op)) {
 			continue;
 		}
 		TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
 		TAILQ_INSERT_AFTER(&vnode_list, vp, mvp, v_vnodelist);
 		if (__predict_false(vp->v_type == VBAD || vp->v_type == VNON)) {
-			VI_UNLOCK(vp);
 			continue;
 		}
-		vholdl(vp);
+		vhold(vp);
 		count--;
 		mtx_unlock(&vnode_list_mtx);
-		VI_UNLOCK(vp);
 		vtryrecycle(vp);
-		vdrop(vp);
 		mtx_lock(&vnode_list_mtx);
 		goto restart;
 	}
@@ -1520,6 +1505,7 @@ vtryrecycle(struct vnode *vp)
 		CTR2(KTR_VFS,
 		    "%s: impossible to recycle, vp %p lock is already held",
 		    __func__, vp);
+		vdrop(vp);
 		return (EWOULDBLOCK);
 	}
 	/*
@@ -1530,6 +1516,7 @@ vtryrecycle(struct vnode *vp)
 		CTR2(KTR_VFS,
 		    "%s: impossible to recycle, cannot start the write for %p",
 		    __func__, vp);
+		vdrop(vp);
 		return (EBUSY);
 	}
 	/*
@@ -1541,7 +1528,7 @@ vtryrecycle(struct vnode *vp)
 	VI_LOCK(vp);
 	if (vp->v_usecount) {
 		VOP_UNLOCK(vp);
-		VI_UNLOCK(vp);
+		vdropl(vp);
 		vn_finished_write(vnmp);
 		CTR2(KTR_VFS,
 		    "%s: impossible to recycle, %p is already referenced",
@@ -1553,7 +1540,7 @@ vtryrecycle(struct vnode *vp)
 		vgonel(vp);
 	}
 	VOP_UNLOCK(vp);
-	VI_UNLOCK(vp);
+	vdropl(vp);
 	vn_finished_write(vnmp);
 	return (0);
 }

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