diff mbox series

[07/17] writeback: Factor writeback_get_batch() out of write_cache_pages()

Message ID 20231218153553.807799-8-hch@lst.de (mailing list archive)
State New
Headers show
Series [01/17] writeback: fix done_index when hitting the wbc->nr_to_write | expand

Commit Message

Christoph Hellwig Dec. 18, 2023, 3:35 p.m. UTC 
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

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.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
[hch: heavily rebased, add helpers to get the tag and end index,
      don't keep the end index in struct writeback_control]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/writeback.h |  1 +
 mm/page-writeback.c       | 49 +++++++++++++++++++++++++--------------
 2 files changed, 32 insertions(+), 18 deletions(-)

Comments

Jan Kara Dec. 21, 2023, 11:17 a.m. UTC | #1 
On Mon 18-12-23 16:35:43, Christoph Hellwig wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> 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.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> [hch: heavily rebased, add helpers to get the tag and end index,
>       don't keep the end index in struct writeback_control]
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Just two nits below. However you decide about them feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

> +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();

I'd prefer to have cond_resched() explicitely in the writeback loop instead
of hidden here in writeback_get_batch() where it logically does not make
too much sense to me...

> +	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
> @@ -2419,38 +2442,30 @@ int write_cache_pages(struct address_space *mapping,
>  		      void *data)
>  {
>  	int error;
> -	int nr_folios;
> -	pgoff_t index;
>  	pgoff_t end;		/* Inclusive */
> -	xa_mark_t tag;
>  
>  	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;
>  	}

Maybe we should have:
	end = wbc_end(wbc);

when we have the helper? But I guess this gets cleaned up in later patches
anyway so whatever.

								Honza
Christoph Hellwig Dec. 21, 2023, 12:22 p.m. UTC | #2 
On Thu, Dec 21, 2023 at 12:17:43PM +0100, Jan Kara wrote:
> > +static void writeback_get_batch(struct address_space *mapping,
> > +		struct writeback_control *wbc)
> > +{
> > +	folio_batch_release(&wbc->fbatch);
> > +	cond_resched();
> 
> I'd prefer to have cond_resched() explicitely in the writeback loop instead
> of hidden here in writeback_get_batch() where it logically does not make
> too much sense to me...

Based on the final state after this series, where would you place it?

(That beeing said there is a discussion underway on lkml to maybe
 kill cond_resched entirely as part of sorting out the preemption
 model mess, at that point this would become a moot point anyway)

> >  	} else {
> > -		index = wbc->range_start >> PAGE_SHIFT;
> > +		wbc->index = wbc->range_start >> PAGE_SHIFT;
> >  		end = wbc->range_end >> PAGE_SHIFT;
> >  	}
> 
> Maybe we should have:
> 	end = wbc_end(wbc);
> 
> when we have the helper? But I guess this gets cleaned up in later patches
> anyway so whatever.

Yeah, this end just goes away.  I can convert it here, but that feels
like pointless churn to me.
Jan Kara Dec. 21, 2023, 12:30 p.m. UTC | #3 
On Thu 21-12-23 13:22:33, Christoph Hellwig wrote:
> On Thu, Dec 21, 2023 at 12:17:43PM +0100, Jan Kara wrote:
> > > +static void writeback_get_batch(struct address_space *mapping,
> > > +		struct writeback_control *wbc)
> > > +{
> > > +	folio_batch_release(&wbc->fbatch);
> > > +	cond_resched();
> > 
> > I'd prefer to have cond_resched() explicitely in the writeback loop instead
> > of hidden here in writeback_get_batch() where it logically does not make
> > too much sense to me...
> 
> Based on the final state after this series, where would you place it?

I guess writeback_get_folio() would be fine... Which is where it naturally
lands with the inlining I already suggested so probably nothing to do here.

> (That beeing said there is a discussion underway on lkml to maybe
>  kill cond_resched entirely as part of sorting out the preemption
>  model mess, at that point this would become a moot point anyway)
> 
> > >  	} else {
> > > -		index = wbc->range_start >> PAGE_SHIFT;
> > > +		wbc->index = wbc->range_start >> PAGE_SHIFT;
> > >  		end = wbc->range_end >> PAGE_SHIFT;
> > >  	}
> > 
> > Maybe we should have:
> > 	end = wbc_end(wbc);
> > 
> > when we have the helper? But I guess this gets cleaned up in later patches
> > anyway so whatever.
> 
> Yeah, this end just goes away.  I can convert it here, but that feels
> like pointless churn to me.

Agreed. Just leave it alone.

								Honza
diff mbox series

Patch

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 390f2dd03cf27e..195393981ccb5c 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -81,6 +81,7 @@  struct writeback_control {
 
 	/* internal fields used by the ->writepages implementation: */
 	struct folio_batch fbatch;
+	pgoff_t index;
 	int err;
 
 #ifdef CONFIG_CGROUP_WRITEBACK
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 564d5faf562ba7..798e5264dc0353 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2383,6 +2383,29 @@  static void writeback_finish(struct address_space *mapping,
 	}
 }
 
+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
@@ -2419,38 +2442,30 @@  int write_cache_pages(struct address_space *mapping,
 		      void *data)
 {
 	int error;
-	int nr_folios;
-	pgoff_t index;
 	pgoff_t end;		/* Inclusive */
-	xa_mark_t tag;
 
 	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;
-	}
+	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
+		tag_pages_for_writeback(mapping, wbc->index, end);
 
 	folio_batch_init(&wbc->fbatch);
 	wbc->err = 0;
 
-	while (index <= end) {
+	while (wbc->index <= end) {
 		int i;
 
-		nr_folios = filemap_get_folios_tag(mapping, &index, end,
-				tag, &wbc->fbatch);
+		writeback_get_batch(mapping, wbc);
 
-		if (nr_folios == 0)
+		if (wbc->fbatch.nr == 0)
 			break;
 
-		for (i = 0; i < nr_folios; i++) {
+		for (i = 0; i < wbc->fbatch.nr; i++) {
 			struct folio *folio = wbc->fbatch.folios[i];
 			unsigned long nr;
 
@@ -2525,8 +2540,6 @@  int write_cache_pages(struct address_space *mapping,
 				return error;
 			}
 		}
-		folio_batch_release(&wbc->fbatch);
-		cond_resched();
 	}
 
 	writeback_finish(mapping, wbc, 0);