From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] zram: introduce per-device debug_stat sysfs node
Date: Fri, 13 May 2016 16:05:53 +0900 [thread overview]
Message-ID: <20160513070553.GC615@swordfish> (raw)
In-Reply-To: <20160513065805.GB615@swordfish>
On (05/13/16 15:58), Sergey Senozhatsky wrote:
> On (05/13/16 15:23), Minchan Kim wrote:
> [..]
> > @@ -737,12 +737,12 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> > zcomp_strm_release(zram->comp, zstrm);
> > zstrm = NULL;
> >
> > - atomic64_inc(&zram->stats.num_recompress);
> > -
> > handle = zs_malloc(meta->mem_pool, clen,
> > GFP_NOIO | __GFP_HIGHMEM);
> > - if (handle)
> > + if (handle) {
> > + atomic64_inc(&zram->stats.num_recompress);
> > goto compress_again;
> > + }
>
> not like a real concern...
>
> the main (and only) purpose of num_recompress is to match performance
> slowdowns and failed fast write paths (when the first zs_malloc() fails).
> this matching is depending on successful second zs_malloc(), but if it's
> also unsuccessful we would only increase failed_writes; w/o increasing
> the failed fast write counter, while we actually would have failed fast
> write and extra zs_malloc() [unaccounted in this case]. yet it's probably
> a bit unlikely to happen, but still. well, just saying.
here I assume that the biggest contributor to re-compress latency is
enabled preemption after zcomp_strm_release() and this second zs_malloc().
the compression itself of a PAGE_SIZE buffer should be fast enough. so IOW
we would pass down the slow path, but would not account it.
-ss
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WARNING: multiple messages have this Message-ID (diff)
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] zram: introduce per-device debug_stat sysfs node
Date: Fri, 13 May 2016 16:05:53 +0900 [thread overview]
Message-ID: <20160513070553.GC615@swordfish> (raw)
In-Reply-To: <20160513065805.GB615@swordfish>
On (05/13/16 15:58), Sergey Senozhatsky wrote:
> On (05/13/16 15:23), Minchan Kim wrote:
> [..]
> > @@ -737,12 +737,12 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> > zcomp_strm_release(zram->comp, zstrm);
> > zstrm = NULL;
> >
> > - atomic64_inc(&zram->stats.num_recompress);
> > -
> > handle = zs_malloc(meta->mem_pool, clen,
> > GFP_NOIO | __GFP_HIGHMEM);
> > - if (handle)
> > + if (handle) {
> > + atomic64_inc(&zram->stats.num_recompress);
> > goto compress_again;
> > + }
>
> not like a real concern...
>
> the main (and only) purpose of num_recompress is to match performance
> slowdowns and failed fast write paths (when the first zs_malloc() fails).
> this matching is depending on successful second zs_malloc(), but if it's
> also unsuccessful we would only increase failed_writes; w/o increasing
> the failed fast write counter, while we actually would have failed fast
> write and extra zs_malloc() [unaccounted in this case]. yet it's probably
> a bit unlikely to happen, but still. well, just saying.
here I assume that the biggest contributor to re-compress latency is
enabled preemption after zcomp_strm_release() and this second zs_malloc().
the compression itself of a PAGE_SIZE buffer should be fast enough. so IOW
we would pass down the slow path, but would not account it.
-ss
next prev parent reply other threads:[~2016-05-13 7:04 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-11 13:45 [PATCH] zram: introduce per-device debug_stat sysfs node Sergey Senozhatsky
2016-05-11 13:45 ` Sergey Senozhatsky
2016-05-12 23:41 ` Minchan Kim
2016-05-12 23:41 ` Minchan Kim
2016-05-13 1:09 ` Sergey Senozhatsky
2016-05-13 1:09 ` Sergey Senozhatsky
2016-05-13 6:23 ` Minchan Kim
2016-05-13 6:23 ` Minchan Kim
2016-05-13 6:58 ` Sergey Senozhatsky
2016-05-13 6:58 ` Sergey Senozhatsky
2016-05-13 7:05 ` Sergey Senozhatsky [this message]
2016-05-13 7:05 ` Sergey Senozhatsky
2016-05-13 7:20 ` Minchan Kim
2016-05-13 7:20 ` Minchan Kim
2016-05-13 7:41 ` Sergey Senozhatsky
2016-05-13 7:41 ` Sergey Senozhatsky
2016-05-13 8:06 ` Sergey Senozhatsky
2016-05-13 8:06 ` Sergey Senozhatsky
2016-05-13 23:05 ` Minchan Kim
2016-05-13 23:05 ` Minchan Kim
2016-05-14 3:37 ` Sergey Senozhatsky
2016-05-14 3:37 ` Sergey Senozhatsky
-- strict thread matches above, loose matches on Subject: below --
2016-05-13 13:03 Sergey Senozhatsky
2016-05-13 23:08 ` Minchan Kim
2016-05-14 3:38 ` Sergey Senozhatsky
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