From: David Rientjes <rientjes@google.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: 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: Wed, 25 Mar 2015 19:37:40 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.10.1503251935180.16714@chino.kir.corp.google.com> (raw)
In-Reply-To: <alpine.LRH.2.02.1503252157330.6657@file01.intranet.prod.int.rdu2.redhat.com>
On Wed, 25 Mar 2015, Mikulas Patocka wrote:
> > Mempools based on slab caches with object constructors are risky because
> > element allocation can happen either from the slab cache itself, meaning
> > the constructor is properly called before returning, or from the mempool
> > reserve pool, meaning the constructor is not called before returning,
> > depending on the allocation context.
>
> I don't think there is any problem. If the allocation is hapenning from
> the slab cache, the constructor is called from the slab sybsystem.
>
> If the allocation is hapenning from the mempool reserve, the constructor
> was called in the past (when the mempool reserve was refilled from the
> cache). So, in both cases, the object allocated frmo the mempool is
> constructed.
>
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).
WARNING: multiple messages have this Message-ID (diff)
From: David Rientjes <rientjes@google.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: 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: Wed, 25 Mar 2015 19:37:40 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.10.1503251935180.16714@chino.kir.corp.google.com> (raw)
In-Reply-To: <alpine.LRH.2.02.1503252157330.6657@file01.intranet.prod.int.rdu2.redhat.com>
On Wed, 25 Mar 2015, Mikulas Patocka wrote:
> > Mempools based on slab caches with object constructors are risky because
> > element allocation can happen either from the slab cache itself, meaning
> > the constructor is properly called before returning, or from the mempool
> > reserve pool, meaning the constructor is not called before returning,
> > depending on the allocation context.
>
> I don't think there is any problem. If the allocation is hapenning from
> the slab cache, the constructor is called from the slab sybsystem.
>
> If the allocation is hapenning from the mempool reserve, the constructor
> was called in the past (when the mempool reserve was refilled from the
> cache). So, in both cases, the object allocated frmo the mempool is
> constructed.
>
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).
--
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next prev parent reply other threads:[~2015-03-26 2:37 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 [this message]
2015-03-26 2:37 ` David Rientjes
2015-03-26 7:28 ` Christoph Hellwig
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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