1 files changed, 23 insertions, 4 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 9e72d04e706e..e8063c938dd2 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -630,6 +630,7 @@ static long wb_writeback(struct bdi_writeback *wb,
         };
         unsigned long oldest_jif;
         long wrote = 0;
+        long write_chunk;
         struct inode *inode;
 
         if (wbc.for_kupdate) {
@@ -642,6 +643,24 @@ static long wb_writeback(struct bdi_writeback *wb,
                 wbc.range_end = LLONG_MAX;
         }
 
+        /*
+         * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
+         * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
+         * here avoids calling into writeback_inodes_wb() more than once.
+         *
+         * The intended call sequence for WB_SYNC_ALL writeback is:
+         *
+         *      wb_writeback()
+         *          __writeback_inodes_sb()     <== called only once
+         *              write_cache_pages()     <== called once for each inode
+         *                   (quickly) tag currently dirty pages
+         *                   (maybe slowly) sync all tagged pages
+         */
+        if (wbc.sync_mode == WB_SYNC_NONE)
+                write_chunk = MAX_WRITEBACK_PAGES;
+        else
+                write_chunk = LONG_MAX;
+
         wbc.wb_start = jiffies; /* livelock avoidance */
         for (;;) {
                 /*
@@ -668,7 +687,7 @@ static long wb_writeback(struct bdi_writeback *wb,
                         break;
 
                 wbc.more_io = 0;
-                wbc.nr_to_write = MAX_WRITEBACK_PAGES;
+                wbc.nr_to_write = write_chunk;
                 wbc.pages_skipped = 0;
 
                 trace_wbc_writeback_start(&wbc, wb->bdi);
@@ -678,8 +697,8 @@ static long wb_writeback(struct bdi_writeback *wb,
                         writeback_inodes_wb(wb, &wbc);
                 trace_wbc_writeback_written(&wbc, wb->bdi);
 
-                work->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
-                wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+                work->nr_pages -= write_chunk - wbc.nr_to_write;
+                wrote += write_chunk - wbc.nr_to_write;
 
                 /*
                  * If we consumed everything, see if we have more
@@ -694,7 +713,7 @@ static long wb_writeback(struct bdi_writeback *wb,
                 /*
                  * Did we write something? Try for more
                  */
-                if (wbc.nr_to_write < MAX_WRITEBACK_PAGES)
+                if (wbc.nr_to_write < write_chunk)
                         continue;
                 /*
                  * Nothing written. Wait for some inode to