On 30/05/2024 17:24, Ofir Gal wrote:
Network drivers are using sendpage_ok() to check the first page of an
iterator in order to disable MSG_SPLICE_PAGES. The iterator can
represent list of contiguous pages.
When MSG_SPLICE_PAGES is enabled skb_splice_from_iter() is being used,
it requires all pages in the iterator to be sendable. Therefore it needs
to check that each page is sendable.
The patch introduces a helper sendpages_ok(), it returns true if all the
contiguous pages are sendable.
Drivers who want to send contiguous pages with MSG_SPLICE_PAGES may use
this helper to check whether the page list is OK. If the helper does not
return true, the driver should remove MSG_SPLICE_PAGES flag.
Signed-off-by: Ofir Gal <ofir.gal@xxxxxxxxxxx>
---
include/linux/net.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/include/linux/net.h b/include/linux/net.h
index 688320b79fcc..b33bdc3e2031 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -322,6 +322,26 @@ static inline bool sendpage_ok(struct page *page)
return !PageSlab(page) && page_count(page) >= 1;
}
+/*
+ * Check sendpage_ok on contiguous pages.
+ */
+static inline bool sendpages_ok(struct page *page, size_t len, size_t offset)
+{
+ unsigned int pagecount;
+ size_t page_offset;
+ int k;
+
+ page = page + offset / PAGE_SIZE;
+ page_offset = offset % PAGE_SIZE;
lets not modify the input page variable.
p = page + offset >> PAGE_SHIFT;
poffset = offset & PAGE_MASK;
+ pagecount = DIV_ROUND_UP(len + page_offset, PAGE_SIZE);
+
+ for (k = 0; k < pagecount; k++)
+ if (!sendpage_ok(page + k))
+ return false;
perhaps instead of doing a costly DIV_ROUND_UP for every network send we
can do:
count = 0;
while (count < len) {
if (!sendpage_ok(p))
return false;
page++;
count += PAGE_SIZE;
}
And we can lose page_offset.
It can be done in a number of ways, but we should be able to do it
without the DIV_ROUND_UP...
I still don't understand how a page in the middle of a contiguous range ends
up coming from the slab while others don't.
Ofir, can you please check which condition in sendpage_ok actually fails?
