2022-10-18 20:31:23

by Pavel Begunkov

Subject: [RFC for-next v2 2/4] bio: split pcpu cache part of bio_put into a helper

Extract a helper out of bio_put for recycling into percpu caches.
It's a preparation patch without functional changes.

Signed-off-by: Pavel Begunkov <[email protected]>
---
block/bio.c | 38 +++++++++++++++++++++++++-------------
1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 5b4594daa259..ac16cc154476 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -725,6 +725,28 @@ static void bio_alloc_cache_destroy(struct bio_set *bs)
bs->cache = NULL;
}

+static inline void bio_put_percpu_cache(struct bio *bio)
+{
+ struct bio_alloc_cache *cache;
+
+ cache = per_cpu_ptr(bio->bi_pool->cache, get_cpu());
+ bio_uninit(bio);
+
+ if ((bio->bi_opf & REQ_POLLED) && !WARN_ON_ONCE(in_interrupt())) {
+ bio->bi_next = cache->free_list;
+ cache->free_list = bio;
+ cache->nr++;
+ } else {
+ put_cpu();
+ bio_free(bio);
+ return;
+ }
+
+ if (cache->nr > ALLOC_CACHE_MAX + ALLOC_CACHE_SLACK)
+ bio_alloc_cache_prune(cache, ALLOC_CACHE_SLACK);
+ put_cpu();
+}
+
/**
* bio_put - release a reference to a bio
* @bio: bio to release reference to
@@ -740,20 +762,10 @@ void bio_put(struct bio *bio)
if (!atomic_dec_and_test(&bio->__bi_cnt))
return;
}
-
- if ((bio->bi_opf & REQ_ALLOC_CACHE) && !WARN_ON_ONCE(in_interrupt())) {
- struct bio_alloc_cache *cache;
-
- bio_uninit(bio);
- cache = per_cpu_ptr(bio->bi_pool->cache, get_cpu());
- bio->bi_next = cache->free_list;
- cache->free_list = bio;
- if (++cache->nr > ALLOC_CACHE_MAX + ALLOC_CACHE_SLACK)
- bio_alloc_cache_prune(cache, ALLOC_CACHE_SLACK);
- put_cpu();
- } else {
+ if (bio->bi_opf & REQ_ALLOC_CACHE)
+ bio_put_percpu_cache(bio);
+ else
bio_free(bio);
- }
}
EXPORT_SYMBOL(bio_put);

--
2.38.0

2022-10-20 08:36:43

by Christoph Hellwig

Subject: Re: [RFC for-next v2 2/4] bio: split pcpu cache part of bio_put into a helper

> + if ((bio->bi_opf & REQ_POLLED) && !WARN_ON_ONCE(in_interrupt())) {
> + bio->bi_next = cache->free_list;
> + cache->free_list = bio;
> + cache->nr++;
> + } else {
> + put_cpu();
> + bio_free(bio);
> + return;
> + }

This reads a little strange with the return in an else. Why not:

if (!(bio->bi_opf & REQ_POLLED) || WARN_ON_ONCE(in_interrupt())) {
put_cpu();
bio_free(bio);
return;
}

bio->bi_next = cache->free_list;
cache->free_list = bio;
cache->nr++;

but given that the simple free case doesn't care about what CPU we're
on or the per-cpu cache pointer, I think we can simply move the

cache = per_cpu_ptr(bio->bi_pool->cache, get_cpu());

after the above return as well.