[07/17] writeback: Factor writeback_get_batch() out of write_cache_pages()
Commit Message
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
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
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.
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
@@ -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
@@ -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);