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From:   Jeff Moyer <jmoyer@redhat.com>
To:     Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc:     bcrl@kvack.org, viro@zeniv.linux.org.uk, linux-aio@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-janitors@vger.kernel.org
Subject: Re: [PATCH] aio: Save a few cycles in 'lookup_ioctx()'
References: <0c3fcdaec33bb12b2367860dfab7ed4224ea000c.1635974999.git.christophe.jaillet@wanadoo.fr>
        <a8666743-4dc5-79b8-56c7-23c05fc88d66@wanadoo.fr>
Date:   Mon, 15 Aug 2022 14:10:49 -0400
In-Reply-To: <a8666743-4dc5-79b8-56c7-23c05fc88d66@wanadoo.fr> (Christophe
        JAILLET's message of "Fri, 12 Aug 2022 06:54:09 +0200")
Message-ID: <x49czd1xtqu.fsf@segfault.boston.devel.redhat.com>
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Christophe JAILLET <christophe.jaillet@wanadoo.fr> writes:

> Le 03/11/2021 =C3=A0 22:31, Christophe JAILLET a =C3=A9crit=C2=A0:
>> Use 'percpu_ref_tryget_live_rcu()' instead of 'percpu_ref_tryget_live()'=
 to
>> save a few cycles when it is known that the rcu lock is already
>> taken/released.
>>
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
>> ---
>>   fs/aio.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/aio.c b/fs/aio.c
>> index 9c81cf611d65..d189ea13e10a 100644
>> --- a/fs/aio.c
>> +++ b/fs/aio.c
>> @@ -1062,7 +1062,7 @@ static struct kioctx *lookup_ioctx(unsigned long c=
tx_id)
>>   	id =3D array_index_nospec(id, table->nr);
>>   	ctx =3D rcu_dereference(table->table[id]);
>>   	if (ctx && ctx->user_id =3D=3D ctx_id) {
>> -		if (percpu_ref_tryget_live(&ctx->users))
>> +		if (percpu_ref_tryget_live_rcu(&ctx->users))
>>   			ret =3D ctx;
>>   	}
>>   out:
>
>
> Hi,
> gentle reminder.
>
> Is this patch useful?
> When I first posted it, percpu_ref_tryget_live_rcu() was really new.
> Now it is part of linux since 5.16.
>
> Saving a few cycles in a function with "lookup" in its name looks
> always good to me.

The patch looks fine to me.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>