On 08.07.25 01:27, Joanne Koong wrote:
On Fri, Jul 4, 2025 at 3:24 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
On 26.04.25 02:08, Joanne Koong wrote:
Optimize processing folios larger than one page size for the direct io
case. If contiguous pages are part of the same folio, collate the
processing instead of processing each page in the folio separately.
Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
fs/fuse/file.c | 55 +++++++++++++++++++++++++++++++++++++-------------
1 file changed, 41 insertions(+), 14 deletions(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 9a31f2a516b9..61eaec1c993b 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1490,7 +1490,8 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
}
while (nbytes < *nbytesp && nr_pages < max_pages) {
- unsigned nfolios, i;
+ struct folio *prev_folio = NULL;
+ unsigned npages, i;
size_t start;
ret = iov_iter_extract_pages(ii, &pages,
@@ -1502,23 +1503,49 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
nbytes += ret;
- nfolios = DIV_ROUND_UP(ret + start, PAGE_SIZE);
+ npages = DIV_ROUND_UP(ret + start, PAGE_SIZE);
- for (i = 0; i < nfolios; i++) {
- struct folio *folio = page_folio(pages[i]);
- unsigned int offset = start +
- (folio_page_idx(folio, pages[i]) << PAGE_SHIFT);
- unsigned int len = min_t(unsigned int, ret, PAGE_SIZE - start);
+ /*
+ * We must check each extracted page. We can't assume every page
+ * in a large folio is used. For example, userspace may mmap() a
+ * file PROT_WRITE, MAP_PRIVATE, and then store to the middle of
+ * a large folio, in which case the extracted pages could be
+ *
+ * folio A page 0
+ * folio A page 1
+ * folio B page 0
+ * folio A page 3
+ *
+ * where folio A belongs to the file and folio B is an anonymous
+ * COW page.
+ */
+ for (i = 0; i < npages && ret; i++) {
+ struct folio *folio;
+ unsigned int offset;
+ unsigned int len;
+
+ WARN_ON(!pages[i]);
+ folio = page_folio(pages[i]);
+
+ len = min_t(unsigned int, ret, PAGE_SIZE - start);
+
+ if (folio == prev_folio && pages[i] != pages[i - 1]) {
I don't really understand the "pages[i] != pages[i - 1]" part.
Why would you have to equal page pointers in there?
The pages extracted are user pages from a userspace iovec. AFAICT,
there's the possibility, eg if userspace mmaps() the file with
copy-on-write, that the same physical page could back multiple
contiguous virtual addresses.
Yes, I but I was rather curious why that would be a condition we are
checking. It's quite the ... corner case :)
Something that might be simpler to understand and implement would be using
num_pages_contiguous()
from
https://lore.kernel.org/all/20250704062602.33500-2-lizhe.67@xxxxxxxxxxxxx/T/#u
and then just making sure that we don't exceed the current folio, if we
ever get contiguous pages that cross a folio.
Thanks for the link. I think here it's common that the pages array
would hold pages from multiple different folios, so maybe a new helper
num_pages_contiguous_folio() would be useful to return back the number
of contiguous pages that are within the scope of the same folio.
Yes, something like that can be useful.
--
Cheers,
David / dhildenb
