writeback: factor writeback_get_batch() out of write_cache_pages()

This simple helper will be the basis of the writeback iterator.  To make
this work, we need to remember the current index and end positions in
writeback_control.

[hch@lst.de: heavily rebased, add helpers to get the tag and end index, don't keep the end index in struct writeback_control]
Link: https://lkml.kernel.org/r/20240215063649.2164017-9-hch@lst.de
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Dave Chinner <dchinner@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 4b8cf9e4810bad4abb295a2776bb7ab6e213268b..f67b3ea866a0fb272b94c423282a5a2b79fa4751 100644 (file)
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -11,6 +11,7 @@
 #include <linux/flex_proportions.h>
 #include <linux/backing-dev-defs.h>
 #include <linux/blk_types.h>
+#include <linux/pagevec.h>
 
 struct bio;
 
@@ -40,6 +41,7 @@ enum writeback_sync_modes {
  * in a manner such that unspecified fields are set to zero.
  */
 struct writeback_control {
+       /* public fields that can be set and/or consumed by the caller: */
        long nr_to_write;               /* Write this many pages, and decrement
                                           this for each page written */
        long pages_skipped;             /* Pages which were not written */
@@ -77,6 +79,10 @@ struct writeback_control {
         */
        struct swap_iocb **swap_plug;
 
+       /* internal fields used by the ->writepages implementation: */
+       struct folio_batch fbatch;
+       pgoff_t index;
+
 #ifdef CONFIG_CGROUP_WRITEBACK
        struct bdi_writeback *wb;       /* wb this writeback is issued under */
        struct inode *inode;            /* inode being written out */

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 4bc55ce9597d13371c412b3fea5dcfb6d1e5e112..5b8dbbef7137224f0c4d23f19df62feab8190cb5 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2392,6 +2392,29 @@ static bool folio_prepare_writeback(struct address_space *mapping,
        return true;
 }
 
+static xa_mark_t wbc_to_tag(struct writeback_control *wbc)
+{
+       if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+               return PAGECACHE_TAG_TOWRITE;
+       return PAGECACHE_TAG_DIRTY;
+}
+
+static pgoff_t wbc_end(struct writeback_control *wbc)
+{
+       if (wbc->range_cyclic)
+               return -1;
+       return wbc->range_end >> PAGE_SHIFT;
+}
+
+static void writeback_get_batch(struct address_space *mapping,
+               struct writeback_control *wbc)
+{
+       folio_batch_release(&wbc->fbatch);
+       cond_resched();
+       filemap_get_folios_tag(mapping, &wbc->index, wbc_end(wbc),
+                       wbc_to_tag(wbc), &wbc->fbatch);
+}
+
 /**
  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
  * @mapping: address space structure to write
@@ -2429,38 +2452,32 @@ int write_cache_pages(struct address_space *mapping,
 {
        int ret = 0;
        int error;
-       struct folio_batch fbatch;
        struct folio *folio;
-       int nr_folios;
-       pgoff_t index;
        pgoff_t end;            /* Inclusive */
-       xa_mark_t tag;
 
-       folio_batch_init(&fbatch);
        if (wbc->range_cyclic) {
-               index = mapping->writeback_index; /* prev offset */
+               wbc->index = mapping->writeback_index; /* prev offset */
                end = -1;
        } else {
-               index = wbc->range_start >> PAGE_SHIFT;
+               wbc->index = wbc->range_start >> PAGE_SHIFT;
                end = wbc->range_end >> PAGE_SHIFT;
        }
-       if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
-               tag_pages_for_writeback(mapping, index, end);
-               tag = PAGECACHE_TAG_TOWRITE;
-       } else {
-               tag = PAGECACHE_TAG_DIRTY;
-       }
-       while (index <= end) {
+       if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+               tag_pages_for_writeback(mapping, wbc->index, end);
+
+       folio_batch_init(&wbc->fbatch);
+
+       while (wbc->index <= end) {
                int i;
 
-               nr_folios = filemap_get_folios_tag(mapping, &index, end,
-                               tag, &fbatch);
+               writeback_get_batch(mapping, wbc);
 
-               if (nr_folios == 0)
+               if (wbc->fbatch.nr == 0)
                        break;
 
-               for (i = 0; i < nr_folios; i++) {
-                       folio = fbatch.folios[i];
+               for (i = 0; i < wbc->fbatch.nr; i++) {
+                       folio = wbc->fbatch.folios[i];
+
                        folio_lock(folio);
                        if (!folio_prepare_writeback(mapping, wbc, folio)) {
                                folio_unlock(folio);
@@ -2498,8 +2515,6 @@ int write_cache_pages(struct address_space *mapping,
                                        goto done;
                        }
                }
-               folio_batch_release(&fbatch);
-               cond_resched();
        }
 
        /*
@@ -2512,6 +2527,7 @@ int write_cache_pages(struct address_space *mapping,
         * of the file if we are called again, which can only happen due to
         * -ENOMEM from the file system.
         */
+       folio_batch_release(&wbc->fbatch);
        if (wbc->range_cyclic)
                mapping->writeback_index = 0;
        return ret;
@@ -2519,7 +2535,7 @@ int write_cache_pages(struct address_space *mapping,
 done:
        if (wbc->range_cyclic)
                mapping->writeback_index = folio->index + folio_nr_pages(folio);
-       folio_batch_release(&fbatch);
+       folio_batch_release(&wbc->fbatch);
        return error;
 }
 EXPORT_SYMBOL(write_cache_pages);