Re: [PATCH v2 1/4] net: introduce helper sendpages_ok()

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 





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?




[Index of Archives]     [Linux RAID]     [Linux SCSI]     [Linux ATA RAID]     [IDE]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Device Mapper]

  Powered by Linux