From: Minchan Kim <minchan@kernel.org>
To: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Nitin Gupta <ngupta@vflare.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Dan Magenheimer <dan.magenheimer@oracle.com>,
Robert Jennings <rcj@linux.vnet.ibm.com>,
Jenifer Hopper <jhopper@us.ibm.com>, Mel Gorman <mgorman@suse.de>,
Johannes Weiner <jweiner@redhat.com>,
Rik van Riel <riel@redhat.com>,
Larry Woodman <lwoodman@redhat.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Dave Hansen <dave@linux.vnet.ibm.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
devel@driverdev.osuosl.org
Subject: Re: [PATCHv4 2/7] zsmalloc: promote to lib/
Date: Thu, 31 Jan 2013 14:35:54 +0900 [thread overview]
Message-ID: <20130131053554.GD23548@blaptop> (raw)
In-Reply-To: <51094A39.8050206@linux.vnet.ibm.com>
On Wed, Jan 30, 2013 at 10:28:41AM -0600, Seth Jennings wrote:
> On 01/29/2013 04:51 PM, Andrew Morton wrote:
> > On Tue, 29 Jan 2013 15:40:22 -0600
> > Seth Jennings <sjenning@linux.vnet.ibm.com> wrote:
> >
> >> This patch promotes the slab-based zsmalloc memory allocator
> >> from the staging tree to lib/
> >
> > Hate to rain on the parade, but... we haven't reviewed zsmalloc
> > yet. At least, I haven't, and I haven't seen others do so.
> >
> > So how's about we forget that zsmalloc was previously in staging and
> > send the zsmalloc code out for review? With a very good changelog
> > explaining why it exists, what problems it solves, etc.
> >
> >
> > I peeked.
> >
> > Don't answer any of the below questions - they are examples of
> > concepts which should be accessible to readers of the
> > hopefully-forthcoming very-good-changelog.
> >
> > - kmap_atomic() returns a void* - there's no need to cast its return value.
> >
> > - Remove private MAX(), use the (much better implemented) max().
> >
> > - It says "This was one of the major issues with its predecessor
> > (xvmalloc)", but drivers/staging/ramster/xvmalloc.c is still in the tree.
> >
> > - USE_PGTABLE_MAPPING should be done via Kconfig.
> >
> > - USE_PGTABLE_MAPPING is interesting and the changelog should go into
> > some details. What are the pros and cons here? Why do the two
> > options exist? Can we eliminate one mode or the other?
> >
> > - Various functions are obscure and would benefit from explanatory
> > comments. Good comments explain "why it exists", more than "what it
> > does".
> >
> > These include get_size_class_index, get_fullness_group,
> > insert_zspage, remove_zspage, fix_fullness_group.
> >
> > Also a description of this handle encoding thing - what do these
> > "handles" refer to? Why is stuff being encoded into them and how?
> >
> > - I don't understand how the whole thing works :( If I allocate a
> > 16 kbyte object with zs_malloc(), what do I get? 16k of
> > contiguous memory? How can it do that if
> > USE_PGTABLE_MAPPING=false? Obviously it can't so it's doing
> > something else. But what?
> >
> > - What does zs_create_pool() do and how do I use it? It appears
> > to create a pool of all possible object sizes. But why do we need
> > more than one such pool kernel-wide?
> >
> > - I tried to work out the actual value of ZS_SIZE_CLASSES but it
> > made my head spin.
> >
> > - We really really don't want to merge zsmalloc! It would be far
> > better to use an existing allocator (perhaps after modifying it)
> > than to add yet another new one. The really-good-changelog should
> > be compelling on this point, please.
> >
> > See, I (and I assume others) are totally on first base here and we need
> > to get through this before we can get onto zswap. Sorry.
> > drivers/staging is where code goes to be ignored :(
>
> I've noticed :-/
>
> Thank you very much for your review! I'll work with Nitin and Minchan
> to beef up the documentation so that the answers to your questions are
> more readily apparent in the code/comments.
Actually, Kconfig of USE_PGTABLE_MAPPING is my plan.
Will do it if anyone has no objection.
--
Kind regards,
Minchan Kim
next prev parent reply other threads:[~2013-01-31 5:35 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-29 21:40 [PATCHv4 0/7] zswap: compressed swap caching Seth Jennings
2013-01-29 21:40 ` [PATCHv4 1/7] debugfs: add get/set for atomic types Seth Jennings
2013-01-29 21:40 ` [PATCHv4 2/7] zsmalloc: promote to lib/ Seth Jennings
2013-01-29 22:51 ` Andrew Morton
2013-01-30 16:28 ` Seth Jennings
2013-01-30 23:34 ` Andrew Morton
2013-01-31 5:35 ` Minchan Kim [this message]
2013-02-13 16:00 ` Seth Jennings
2013-01-29 21:40 ` [PATCHv4 3/7] zswap: add to mm/ Seth Jennings
2013-01-31 7:07 ` Minchan Kim
2013-01-31 19:06 ` Seth Jennings
2013-01-31 20:07 ` Robert Jennings
2013-02-01 2:38 ` Minchan Kim
2013-02-01 15:31 ` Seth Jennings
2013-02-01 17:46 ` Seth Jennings
2013-01-29 21:40 ` [PATCHv4 4/7] mm: break up swap_writepage() for frontswap backends Seth Jennings
2013-01-29 21:40 ` [PATCHv4 5/7] mm: allow for outstanding swap writeback accounting Seth Jennings
2013-01-29 21:40 ` [PATCHv4 6/7] zswap: add flushing support Seth Jennings
2013-01-29 23:03 ` Andrew Morton
2013-02-01 7:27 ` Minchan Kim
2013-02-13 6:24 ` Seth Jennings
2013-01-29 21:40 ` [PATCHv4 7/7] zswap: add documentation Seth Jennings
2013-01-29 23:07 ` Andrew Morton
2013-01-29 22:14 ` [PATCHv4 0/7] zswap: compressed swap caching Joe Perches
2013-01-29 22:49 ` Seth Jennings
2013-01-30 4:32 ` Minchan Kim
2013-01-30 16:01 ` Seth Jennings
2013-02-01 1:39 ` Simon Jeons
2013-02-01 15:13 ` Seth Jennings
2013-02-03 0:17 ` Simon Jeons
2013-02-04 14:56 ` Seth Jennings
2013-02-04 1:03 ` Simon Jeons
2013-02-04 15:07 ` Seth Jennings
[not found] ` <5110287A.5050200@linux.vnet.ibm.com>
2013-02-04 21:45 ` Seth Jennings
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