On Fri, Oct 18, 2024 at 4:00 AM Yunsheng Lin [off-list ref] wrote:

Currently there is one 'struct page_frag' for every 'struct
sock' and 'struct task_struct', we are about to replace the
'struct page_frag' with 'struct page_frag_cache' for them.
Before begin the replacing, we need to ensure the size of
'struct page_frag_cache' is not bigger than the size of
'struct page_frag', as there may be tens of thousands of
'struct sock' and 'struct task_struct' instances in the
system.

By or'ing the page order & pfmemalloc with lower bits of
'va' instead of using 'u16' or 'u32' for page size and 'u8'
for pfmemalloc, we are able to avoid 3 or 5 bytes space waste.
And page address & pfmemalloc & order is unchanged for the
same page in the same 'page_frag_cache' instance, it makes
sense to fit them together.

After this patch, the size of 'struct page_frag_cache' should be
the same as the size of 'struct page_frag'.

CC: Alexander Duyck <redacted>
Signed-off-by: Yunsheng Lin <redacted>
---
 include/linux/mm_types_task.h   | 19 +++++----
 include/linux/page_frag_cache.h | 24 ++++++++++-
 mm/page_frag_cache.c            | 70 ++++++++++++++++++++++-----------
 3 files changed, 81 insertions(+), 32 deletions(-)

LGTM

Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>