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rds: Acquire per-CPU pointer within BH disabled section

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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: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20250512092736.229935-15-bigeasy@linutronix.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Sebastian Andrzej Siewior 2025-05-12 11:27:35 +02:00 • committed by Paolo Abeni
parent aaaaa6639c
commit 0af5928f35
1 changed files with 2 additions and 4 deletions
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6
net/rds/page.c
View file

@ -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,