From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Nitin Gupta <ngupta@vflare.org>,
Jerome Marchand <jmarchan@redhat.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Ganesh Mahendran <opensource.ganesh@gmail.com>
Subject: Re: [PATCH v1 2/2] zram: remove init_lock in zram_make_request
Date: Wed, 28 Jan 2015 23:56:51 +0900 [thread overview]
Message-ID: <20150128145651.GB965@swordfish> (raw)
In-Reply-To: <1422432945-6764-2-git-send-email-minchan@kernel.org>
On (01/28/15 17:15), Minchan Kim wrote:
> Admin could reset zram during I/O operation going on so we have
> used zram->init_lock as read-side lock in I/O path to prevent
> sudden zram meta freeing.
>
> However, the init_lock is really troublesome.
> We can't do call zram_meta_alloc under init_lock due to lockdep splat
> because zram_rw_page is one of the function under reclaim path and
> hold it as read_lock while other places in process context hold it
> as write_lock. So, we have used allocation out of the lock to avoid
> lockdep warn but it's not good for readability and fainally, I met
> another lockdep splat between init_lock and cpu_hotpulug from
> kmem_cache_destroy during wokring zsmalloc compaction. :(
>
> Yes, the ideal is to remove horrible init_lock of zram in rw path.
> This patch removes it in rw path and instead, put init_done bool
> variable to check initialization done with smp_[wmb|rmb] and
> srcu_[un]read_lock to prevent sudden zram meta freeing
> during I/O operation.
>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> drivers/block/zram/zram_drv.c | 85 +++++++++++++++++++++++++++++++------------
> drivers/block/zram/zram_drv.h | 5 +++
> 2 files changed, 66 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index a598ada817f0..b33add453027 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -32,6 +32,7 @@
> #include <linux/string.h>
> #include <linux/vmalloc.h>
> #include <linux/err.h>
> +#include <linux/srcu.h>
>
> #include "zram_drv.h"
>
> @@ -53,9 +54,31 @@ static ssize_t name##_show(struct device *d, \
> } \
> static DEVICE_ATTR_RO(name);
>
> -static inline int init_done(struct zram *zram)
> +static inline bool init_done(struct zram *zram)
> {
> - return zram->meta != NULL;
> + /*
> + * init_done can be used without holding zram->init_lock in
> + * read/write handler(ie, zram_make_request) but we should make sure
> + * that zram->init_done should set up after meta initialization is
> + * done. Look at setup_init_done.
> + */
> + bool ret = zram->init_done;
I don't like re-introduced ->init_done.
another idea... how about using `zram->disksize == 0' instead of
`->init_done' (previously `->meta != NULL')? should do the trick.
and I'm not sure I get this rmb...
-ss
next prev parent reply other threads:[~2015-01-28 20:12 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1422432945-6764-1-git-send-email-minchan@kernel.org>
2015-01-28 14:19 ` [PATCH 1/2] zram: free meta table in zram_meta_free Sergey Senozhatsky
2015-01-28 23:17 ` Minchan Kim
2015-01-29 1:49 ` Ganesh Mahendran
[not found] ` <1422432945-6764-2-git-send-email-minchan@kernel.org>
2015-01-28 14:56 ` Sergey Senozhatsky [this message]
2015-01-28 15:04 ` [PATCH v1 2/2] zram: remove init_lock in zram_make_request Sergey Senozhatsky
2015-01-28 23:33 ` Minchan Kim
[not found] ` <CAHqPoqKZFDSjO1pL+ixYe_m_L0nGNcu04qSNp-jd1fUixKtHnw@mail.gmail.com>
2015-01-29 2:01 ` Minchan Kim
2015-01-29 2:22 ` Sergey Senozhatsky
2015-01-29 5:28 ` Minchan Kim
2015-01-29 6:06 ` Sergey Senozhatsky
2015-01-29 6:35 ` Minchan Kim
2015-01-29 7:08 ` Sergey Senozhatsky
2015-01-30 14:41 ` Minchan Kim
2015-01-31 11:31 ` Sergey Senozhatsky
2015-02-01 14:50 ` Sergey Senozhatsky
2015-02-01 15:04 ` Sergey Senozhatsky
2015-02-02 1:43 ` Minchan Kim
2015-02-02 1:59 ` Sergey Senozhatsky
2015-02-02 2:45 ` Minchan Kim
2015-02-02 3:47 ` Sergey Senozhatsky
2015-02-02 1:30 ` Minchan Kim
2015-02-02 1:48 ` Sergey Senozhatsky
2015-02-02 2:44 ` Minchan Kim
2015-02-02 4:01 ` Sergey Senozhatsky
2015-02-02 4:28 ` Minchan Kim
2015-02-02 5:09 ` Sergey Senozhatsky
2015-02-02 5:18 ` Minchan Kim
2015-02-02 5:28 ` Sergey Senozhatsky
2015-02-02 5:10 ` Minchan Kim
2015-01-30 0:20 ` Sergey Senozhatsky
2015-01-29 13:48 ` Ganesh Mahendran
2015-01-29 15:12 ` Sergey Senozhatsky
2015-01-30 7:52 ` Ganesh Mahendran
2015-01-30 8:08 ` Sergey Senozhatsky
2015-01-31 8:50 ` Ganesh Mahendran
2015-01-31 11:07 ` Sergey Senozhatsky
2015-01-31 12:59 ` Ganesh Mahendran
2015-02-02 3:41 Minchan Kim
2015-02-02 5:59 ` Sergey Senozhatsky
2015-02-02 6:18 ` Minchan Kim
2015-02-02 7:06 ` Sergey Senozhatsky
2015-02-03 1:54 ` Sergey Senozhatsky
2015-02-03 3:02 ` Minchan Kim
2015-02-03 3:56 ` Sergey Senozhatsky
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