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From: Christoph Hellwig <hch@lst.de>
To: David Rientjes <rientjes@google.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dave Kleikamp <shaggy@kernel.org>, Christoph Hellwig <hch@lst.de>,
	Sebastian Ott <sebott@linux.vnet.ibm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	jfs-discussion@lists.sourceforge.net
Subject: Re: [patch 1/4] fs, jfs: remove slab object constructor
Date: Thu, 26 Mar 2015 08:28:00 +0100	[thread overview]
Message-ID: <20150326072800.GA26163@lst.de> (raw)
In-Reply-To: <alpine.DEB.2.10.1503251935180.16714@chino.kir.corp.google.com>

On Wed, Mar 25, 2015 at 07:37:40PM -0700, David Rientjes wrote:
> That would be true only for
> 
> 	ptr = mempool_alloc(gfp, pool);
> 	mempool_free(ptr, pool);
> 
> and nothing in between, and that's pretty pointless.  Typically, callers 
> allocate memory, modify it, and then free it.  When that happens with 
> mempools, and we can't allocate slab because of the gfp context, mempools 
> will return elements in the state in which they were freed (modified, not 
> as constructed).

The historic slab allocator (Solaris and early Linux) expects objects
to be returned in the same / similar enough form as the constructor
returned it, and the constructor is only called when allocating pages
from the page pool.

I have to admit that I haven't used this feature forever, and I have no idea if
people changed how the allocator works in the meantime.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: David Rientjes <rientjes@google.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dave Kleikamp <shaggy@kernel.org>, Christoph Hellwig <hch@lst.de>,
	Sebastian Ott <sebott@linux.vnet.ibm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	jfs-discussion@lists.sourceforge.net
Subject: Re: [patch 1/4] fs, jfs: remove slab object constructor
Date: Thu, 26 Mar 2015 08:28:00 +0100	[thread overview]
Message-ID: <20150326072800.GA26163@lst.de> (raw)
In-Reply-To: <alpine.DEB.2.10.1503251935180.16714@chino.kir.corp.google.com>

On Wed, Mar 25, 2015 at 07:37:40PM -0700, David Rientjes wrote:
> That would be true only for
> 
> 	ptr = mempool_alloc(gfp, pool);
> 	mempool_free(ptr, pool);
> 
> and nothing in between, and that's pretty pointless.  Typically, callers 
> allocate memory, modify it, and then free it.  When that happens with 
> mempools, and we can't allocate slab because of the gfp context, mempools 
> will return elements in the state in which they were freed (modified, not 
> as constructed).

The historic slab allocator (Solaris and early Linux) expects objects
to be returned in the same / similar enough form as the constructor
returned it, and the constructor is only called when allocating pages
from the page pool.

I have to admit that I haven't used this feature forever, and I have no idea if
people changed how the allocator works in the meantime.

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  reply	other threads:[~2015-03-26  7:28 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-24 23:08 [patch 1/4] fs, jfs: remove slab object constructor David Rientjes
2015-03-24 23:08 ` David Rientjes
2015-03-24 23:09 ` [patch 2/4] mm, mempool: disallow mempools based on slab caches with constructors David Rientjes
2015-03-24 23:09   ` David Rientjes
2015-03-24 23:09 ` [patch v2 3/4] mm, mempool: poison elements backed by slab allocator David Rientjes
2015-03-24 23:09   ` David Rientjes
2015-03-24 23:10 ` [patch v2 4/4] mm, mempool: poison elements backed by page allocator David Rientjes
2015-03-24 23:10   ` David Rientjes
2015-03-25 21:55   ` Andrew Morton
2015-03-25 21:55     ` Andrew Morton
2015-03-26 16:07     ` Andrey Ryabinin
2015-03-26 16:07       ` Andrey Ryabinin
2015-03-26 20:38   ` Andrey Ryabinin
2015-03-26 20:38     ` Andrey Ryabinin
2015-03-26 22:50     ` David Rientjes
2015-03-26 22:50       ` David Rientjes
2015-03-30  8:53       ` Andrey Ryabinin
2015-03-30  8:53         ` Andrey Ryabinin
2015-03-31 11:33       ` Andrey Ryabinin
2015-03-31 11:33         ` Andrey Ryabinin
2015-04-03  1:04         ` David Rientjes
2015-04-03  1:04           ` David Rientjes
2015-04-03  1:07           ` [patch -mm] mm, mempool: poison elements backed by page allocator fix fix David Rientjes
2015-04-03  1:07             ` David Rientjes
2015-03-24 23:41 ` [patch 1/4] fs, jfs: remove slab object constructor Dave Kleikamp
2015-03-24 23:41   ` Dave Kleikamp
2015-03-26  2:18 ` Mikulas Patocka
2015-03-26  2:18   ` Mikulas Patocka
2015-03-26  2:37   ` David Rientjes
2015-03-26  2:37     ` David Rientjes
2015-03-26  7:28     ` Christoph Hellwig [this message]
2015-03-26  7:28       ` Christoph Hellwig
2015-03-26 14:57       ` Dave Kleikamp
2015-03-26 14:57         ` Dave Kleikamp

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