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Date: Sat, 19 Feb 2022 16:33:44 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Miaohe Lin' <linmiaohe@...wei.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC: "vitaly.wool@...sulko.com" <vitaly.wool@...sulko.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 6/9] mm/z3fold: move decrement of pool->pages_nr into
__release_z3fold_page()
From: Miaohe Lin
> Sent: 19 February 2022 09:26
>
> The z3fold will always do atomic64_dec(&pool->pages_nr) when the
> __release_z3fold_page() is called. Thus we can move decrement of
> pool->pages_nr into __release_z3fold_page() to simplify the code.
> Also we can reduce the size of z3fold.o ~1k.
> Without this patch:
> text data bss dec hex filename
> 15444 1376 8 16828 41bc mm/z3fold.o
> With this patch:
> text data bss dec hex filename
> 15044 1248 8 16300 3fac mm/z3fold.o
I can't see anything obvious in this patch that would reduce the size much.
OTOH there are some large functions that are pointlessly marked 'inline'.
Maybe the compiler made a better choice?
Although it isn't al all obvious why the 'data' size changes.
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
> mm/z3fold.c | 41 ++++++++++++-----------------------------
> 1 file changed, 12 insertions(+), 29 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index adc0b3fa4906..18a697f6fe32 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -520,6 +520,8 @@ static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
> list_add(&zhdr->buddy, &pool->stale);
> queue_work(pool->release_wq, &pool->work);
> spin_unlock(&pool->stale_lock);
> +
> + atomic64_dec(&pool->pages_nr);
Looks like you can move the decrement inside the lock.
If you can do the same for the increment you can avoid the
expensive locked bus cycle.
David
> }
>
> static void release_z3fold_page(struct kref *ref)
> @@ -737,13 +739,9 @@ static struct z3fold_header *compact_single_buddy(struct z3fold_header *zhdr)
> return new_zhdr;
>
> out_fail:
> - if (new_zhdr) {
> - if (kref_put(&new_zhdr->refcount, release_z3fold_page_locked))
> - atomic64_dec(&pool->pages_nr);
> - else {
> - add_to_unbuddied(pool, new_zhdr);
> - z3fold_page_unlock(new_zhdr);
> - }
> + if (new_zhdr && !kref_put(&new_zhdr->refcount, release_z3fold_page_locked)) {
> + add_to_unbuddied(pool, new_zhdr);
> + z3fold_page_unlock(new_zhdr);
> }
> return NULL;
>
> @@ -816,10 +814,8 @@ static void do_compact_page(struct z3fold_header *zhdr, bool locked)
> list_del_init(&zhdr->buddy);
> spin_unlock(&pool->lock);
>
> - if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
> - atomic64_dec(&pool->pages_nr);
> + if (kref_put(&zhdr->refcount, release_z3fold_page_locked))
> return;
> - }
>
> if (test_bit(PAGE_STALE, &page->private) ||
> test_and_set_bit(PAGE_CLAIMED, &page->private)) {
> @@ -829,9 +825,7 @@ static void do_compact_page(struct z3fold_header *zhdr, bool locked)
>
> if (!zhdr->foreign_handles && buddy_single(zhdr) &&
> zhdr->mapped_count == 0 && compact_single_buddy(zhdr)) {
> - if (kref_put(&zhdr->refcount, release_z3fold_page_locked))
> - atomic64_dec(&pool->pages_nr);
> - else {
> + if (!kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
> clear_bit(PAGE_CLAIMED, &page->private);
> z3fold_page_unlock(zhdr);
> }
> @@ -1089,10 +1083,8 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
> if (zhdr) {
> bud = get_free_buddy(zhdr, chunks);
> if (bud == HEADLESS) {
> - if (kref_put(&zhdr->refcount,
> + if (!kref_put(&zhdr->refcount,
> release_z3fold_page_locked))
> - atomic64_dec(&pool->pages_nr);
> - else
> z3fold_page_unlock(zhdr);
> pr_err("No free chunks in unbuddied\n");
> WARN_ON(1);
> @@ -1239,10 +1231,8 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
>
> if (!page_claimed)
> free_handle(handle, zhdr);
> - if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
> - atomic64_dec(&pool->pages_nr);
> + if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list))
> return;
> - }
> if (page_claimed) {
> /* the page has not been claimed by us */
> put_z3fold_header(zhdr);
> @@ -1353,9 +1343,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
> break;
> }
> if (!z3fold_page_trylock(zhdr)) {
> - if (kref_put(&zhdr->refcount,
> - release_z3fold_page))
> - atomic64_dec(&pool->pages_nr);
> + kref_put(&zhdr->refcount, release_z3fold_page);
> zhdr = NULL;
> continue; /* can't evict at this point */
> }
> @@ -1366,10 +1354,8 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
> */
> if (zhdr->foreign_handles ||
> test_and_set_bit(PAGE_CLAIMED, &page->private)) {
> - if (kref_put(&zhdr->refcount,
> + if (!kref_put(&zhdr->refcount,
> release_z3fold_page_locked))
> - atomic64_dec(&pool->pages_nr);
> - else
> z3fold_page_unlock(zhdr);
> zhdr = NULL;
> continue; /* can't evict such page */
> @@ -1447,7 +1433,6 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
> if (kref_put(&zhdr->refcount,
> release_z3fold_page_locked)) {
> kmem_cache_free(pool->c_handle, slots);
> - atomic64_dec(&pool->pages_nr);
> return 0;
> }
> /*
> @@ -1669,10 +1654,8 @@ static void z3fold_page_putback(struct page *page)
> if (!list_empty(&zhdr->buddy))
> list_del_init(&zhdr->buddy);
> INIT_LIST_HEAD(&page->lru);
> - if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
> - atomic64_dec(&pool->pages_nr);
> + if (kref_put(&zhdr->refcount, release_z3fold_page_locked))
> return;
> - }
> spin_lock(&pool->lock);
> list_add(&page->lru, &pool->lru);
> spin_unlock(&pool->lock);
> --
> 2.23.0
-
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