FreeBSD: zfs_putpages: don't undirty pages until after write completes

zfs_putpages() would put the entire range of pages onto the ZIL, then
return VM_PAGER_OK for each page to the kernel. However, an associated
zil_commit() or txg sync had not happened at this point, so the write
may not actually be on disk.

So, we rework it to use a ZIL commit callback, and do the post-write
work of undirtying the page and signaling completion there. We return
VM_PAGER_PEND to the kernel instead so it knows that we will take care
of it.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Mark Johnston <markj@FreeBSD.org>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17445

include/os/freebsd/spl/sys/vm.h

@@ -35,6 +35,7 @@
 extern const int zfs_vm_pagerret_bad;
 extern const int zfs_vm_pagerret_error;
 extern const int zfs_vm_pagerret_ok;
+extern const int zfs_vm_pagerret_pend;
 extern const int zfs_vm_pagerput_sync;
 extern const int zfs_vm_pagerput_inval;
 

module/os/freebsd/spl/spl_vm.c

@@ -43,6 +43,7 @@
 const int zfs_vm_pagerret_bad = VM_PAGER_BAD;
 const int zfs_vm_pagerret_error = VM_PAGER_ERROR;
 const int zfs_vm_pagerret_ok = VM_PAGER_OK;
+const int zfs_vm_pagerret_pend = VM_PAGER_PEND;
 const int zfs_vm_pagerput_sync = VM_PAGER_PUT_SYNC;
 const int zfs_vm_pagerput_inval = VM_PAGER_PUT_INVAL;
 

module/os/freebsd/zfs/zfs_vnops_os.c

@@ -25,6 +25,7 @@
  * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
  * Copyright (c) 2014 Integros [integros.com]
  * Copyright 2017 Nexenta Systems, Inc.
+ * Copyright (c) 2025, Klara, Inc.
  */
 
 /* Portions Copyright 2007 Jeremy Teo */
@@ -4072,6 +4073,33 @@ zfs_freebsd_getpages(struct vop_getpages_args *ap)
 	    ap->a_rahead));
 }
 
+typedef struct {
+	uint_t		pca_npages;
+	vm_page_t	pca_pages[];
+} putpage_commit_arg_t;
+
+static void
+zfs_putpage_commit_cb(void *arg)
+{
+	putpage_commit_arg_t *pca = arg;
+	vm_object_t object = pca->pca_pages[0]->object;
+
+	zfs_vmobject_wlock(object);
+
+	for (uint_t i = 0; i < pca->pca_npages; i++) {
+		vm_page_t pp = pca->pca_pages[i];
+		vm_page_undirty(pp);
+		vm_page_sunbusy(pp);
+	}
+
+	vm_object_pip_wakeupn(object, pca->pca_npages);
+
+	zfs_vmobject_wunlock(object);
+
+	kmem_free(pca,
+	    offsetof(putpage_commit_arg_t, pca_pages[pca->pca_npages]));
+}
+
 static int
 zfs_putpages(struct vnode *vp, vm_page_t *ma, size_t len, int flags,
     int *rtvals)
@@ -4173,10 +4201,12 @@ zfs_putpages(struct vnode *vp, vm_page_t *ma, size_t len, int flags,
 	}
 
 	if (zp->z_blksz < PAGE_SIZE) {
-		for (i = 0; len > 0; off += tocopy, len -= tocopy, i++) {
+		vm_ooffset_t woff = off;
-			tocopy = len > PAGE_SIZE ? PAGE_SIZE : len;
+		size_t wlen = len;
+		for (i = 0; wlen > 0; woff += tocopy, wlen -= tocopy, i++) {
+			tocopy = MIN(PAGE_SIZE, wlen);
 			va = zfs_map_page(ma[i], &sf);
-			dmu_write(zfsvfs->z_os, zp->z_id, off, tocopy, va, tx);
+			dmu_write(zfsvfs->z_os, zp->z_id, woff, tocopy, va, tx);
 			zfs_unmap_page(sf);
 		}
 	} else {
@@ -4197,19 +4227,19 @@ zfs_putpages(struct vnode *vp, vm_page_t *ma, size_t len, int flags,
 		zfs_tstamp_update_setup(zp, CONTENT_MODIFIED, mtime, ctime);
 		err = sa_bulk_update(zp->z_sa_hdl, bulk, count, tx);
 		ASSERT0(err);
-		/*
-		 * XXX we should be passing a callback to undirty
-		 * but that would make the locking messier
-		 */
-		zfs_log_write(zfsvfs->z_log, tx, TX_WRITE, zp, off,
-		    len, commit, B_FALSE, NULL, NULL);
 
-		zfs_vmobject_wlock(object);
+		putpage_commit_arg_t *pca = kmem_alloc(
-		for (i = 0; i < ncount; i++) {
+		    offsetof(putpage_commit_arg_t, pca_pages[ncount]),
-			rtvals[i] = zfs_vm_pagerret_ok;
+		    KM_SLEEP);
-			vm_page_undirty(ma[i]);
+		pca->pca_npages = ncount;
-		}
+		memcpy(pca->pca_pages, ma, sizeof (vm_page_t) * ncount);
-		zfs_vmobject_wunlock(object);
+
+		zfs_log_write(zfsvfs->z_log, tx, TX_WRITE, zp,
+		    off, len, commit, B_FALSE, zfs_putpage_commit_cb, pca);
+
+		for (i = 0; i < ncount; i++)
+			rtvals[i] = zfs_vm_pagerret_pend;
+
 		VM_CNT_INC(v_vnodeout);
 		VM_CNT_ADD(v_vnodepgsout, ncount);
 	}