Commit 0af5928f authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Paolo Abeni
Browse files

rds: Acquire per-CPU pointer within BH disabled section 



rds_page_remainder_alloc() obtains the current CPU with get_cpu() while
disabling preemption. Then the CPU number is used to access the per-CPU
data structure via per_cpu().

This can be optimized by relying on local_bh_disable() to provide a
stable CPU number/ avoid migration and then using this_cpu_ptr() to
retrieve the data structure.

Cc: Allison Henderson <allison.henderson@oracle.com>
Cc: linux-rdma@vger.kernel.org
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20250512092736.229935-15-bigeasy@linutronix.de


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent aaaaa663

net/rds/page.c

+2 −4
Original line number Diff line number Diff line
@@ -86,8 +86,8 @@ int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes, 
		goto out;

	}



	rem = &per_cpu(rds_page_remainders, get_cpu());

	local_bh_disable();

	rem = this_cpu_ptr(&rds_page_remainders);



	while (1) {

		/* avoid a tiny region getting stuck by tossing it */
@@ -116,12 +116,11 @@ int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes, 


		/* alloc if there is nothing for us to use */

		local_bh_enable();

		put_cpu();



		page = alloc_page(gfp);



		rem = &per_cpu(rds_page_remainders, get_cpu());

		local_bh_disable();

		rem = this_cpu_ptr(&rds_page_remainders);



		if (!page) {

			ret = -ENOMEM;
@@ -140,7 +139,6 @@ int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes, 
	}



	local_bh_enable();

	put_cpu();

out:

	rdsdebug("bytes %lu ret %d %p %u %u\n", bytes, ret,

		 ret ? NULL : sg_page(scat), ret ? 0 : scat->offset,