Re: [PATCHv4] driver core/platform: don't leak memory allocated for dma_mask
On Sun, Feb 09, 2014 at 10:30:32AM +0100, Uwe Kleine-König wrote: > Hello Yann, > > On Sun, Feb 09, 2014 at 08:47:22AM +0100, Yann Droneaud wrote: > > Hi, > > > > Le samedi 08 février 2014 à 16:09 +0100, Uwe Kleine-König a écrit : > > > On Fri, Feb 07, 2014 at 03:20:05PM -0800, Greg Kroah-Hartman wrote: > > > > On Mon, Jan 27, 2014 at 11:05:52AM +0100, Yann Droneaud wrote: > > > > > Since commit 01dcc60a7cb8, platform_device_register_full() is > > > > > available to allocate and register a platform device. > > > > > > > > > > If a dma_mask is provided as part of platform_device_info, > > > > > platform_device_register_full() allocate memory for a u64 using > > > > > kmalloc(). > > > > > > > > > > A comment in the code state that "[t]his memory isn't freed when the > > > > > device is put". > > > > > > > > > > It's never a good thing to leak memory, but there's only very few > > > > > users of platform_device_info's dma_mask, and those are mostly > > > > > "static" devices that are not going to be plugged/unplugged often. > > > > > > > > > > So memory leak is not really an issue, but allocating 8 bytes through > > > > > kmalloc() seems overkill. > > > > > > > > > > And it's a pity to have to allocate 8 bytes for the dma_mask while up > > > > > to 7 bytes are wasted at the end of struct platform_object in the form > > > > > of padding after name field: unfortunately this padding is not used > > > > > when allocating the memory to hold the name. > > > > > > > > > > To address theses issues, this patch adds dma_mask to platform_object > > > > > struct so that it is always allocated for all struct platform_device > > > > > allocated through platform_device_alloc() or > > > > > platform_device_register_full(). > > > > > And since it's within struct platform_object, dma_mask won't be leaked > > > > > anymore when struct platform_device got released. Storage for dma_mask > > > > > is added almost for free by removing the padding at the end of struct > > > > > platform_object. > > > > > How does the padding of name change? The only thing that I see changing > > > for .name is that it's a char[] now instead of a char[1]. As it was > > > used as a flexible array already before the padding (which only applies > > > to a stand alone struct platform_object) doesn't matter. > > > I guess that is a tool problem that still some padding changes are > > > reported? > > > > > > > When name is defined as char name[1] at the end of the structure, the > > compiler is required to add padding after it (since the structure is not > > "packed" through some compiler extension). > > This padding is added in order to have a size multiple of the highest > > required alignement for types insided the structure. This is required so > > that each item of an array of "struct platform_object" are aligned. > > > > Changing name[1] to name[0] or name[] free the compiler from adding > > storage space for name and thus remove the need for padding after it. > Ah, I see, even though .name was used as a flexible array there was too > much allocated because sizeof(struct platform_object) includes the 7 > bytes of padding. > > Maybe it makes sense to split the patch into a) s/name[1]/name[]/ and b) > add dma_mask? Up to you, you can have my Ack also for the single patch. > > Acked-by: Uwe Kleine-König Breaking it up would be good, if for no other reason than people got confused with it as-is. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCHv4] driver core/platform: don't leak memory allocated for dma_mask
Hello Yann, On Sun, Feb 09, 2014 at 08:47:22AM +0100, Yann Droneaud wrote: > Hi, > > Le samedi 08 février 2014 à 16:09 +0100, Uwe Kleine-König a écrit : > > On Fri, Feb 07, 2014 at 03:20:05PM -0800, Greg Kroah-Hartman wrote: > > > On Mon, Jan 27, 2014 at 11:05:52AM +0100, Yann Droneaud wrote: > > > > Since commit 01dcc60a7cb8, platform_device_register_full() is > > > > available to allocate and register a platform device. > > > > > > > > If a dma_mask is provided as part of platform_device_info, > > > > platform_device_register_full() allocate memory for a u64 using > > > > kmalloc(). > > > > > > > > A comment in the code state that "[t]his memory isn't freed when the > > > > device is put". > > > > > > > > It's never a good thing to leak memory, but there's only very few > > > > users of platform_device_info's dma_mask, and those are mostly > > > > "static" devices that are not going to be plugged/unplugged often. > > > > > > > > So memory leak is not really an issue, but allocating 8 bytes through > > > > kmalloc() seems overkill. > > > > > > > > And it's a pity to have to allocate 8 bytes for the dma_mask while up > > > > to 7 bytes are wasted at the end of struct platform_object in the form > > > > of padding after name field: unfortunately this padding is not used > > > > when allocating the memory to hold the name. > > > > > > > > To address theses issues, this patch adds dma_mask to platform_object > > > > struct so that it is always allocated for all struct platform_device > > > > allocated through platform_device_alloc() or > > > > platform_device_register_full(). > > > > And since it's within struct platform_object, dma_mask won't be leaked > > > > anymore when struct platform_device got released. Storage for dma_mask > > > > is added almost for free by removing the padding at the end of struct > > > > platform_object. > > > How does the padding of name change? The only thing that I see changing > > for .name is that it's a char[] now instead of a char[1]. As it was > > used as a flexible array already before the padding (which only applies > > to a stand alone struct platform_object) doesn't matter. > > I guess that is a tool problem that still some padding changes are > > reported? > > > > When name is defined as char name[1] at the end of the structure, the > compiler is required to add padding after it (since the structure is not > "packed" through some compiler extension). > This padding is added in order to have a size multiple of the highest > required alignement for types insided the structure. This is required so > that each item of an array of "struct platform_object" are aligned. > > Changing name[1] to name[0] or name[] free the compiler from adding > storage space for name and thus remove the need for padding after it. Ah, I see, even though .name was used as a flexible array there was too much allocated because sizeof(struct platform_object) includes the 7 bytes of padding. Maybe it makes sense to split the patch into a) s/name[1]/name[]/ and b) add dma_mask? Up to you, you can have my Ack also for the single patch. Acked-by: Uwe Kleine-König Thanks Uwe -- Pengutronix e.K. | Uwe Kleine-König| Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCHv4] driver core/platform: don't leak memory allocated for dma_mask
Hi, Le samedi 08 février 2014 à 16:09 +0100, Uwe Kleine-König a écrit : > On Fri, Feb 07, 2014 at 03:20:05PM -0800, Greg Kroah-Hartman wrote: > > On Mon, Jan 27, 2014 at 11:05:52AM +0100, Yann Droneaud wrote: > > > Since commit 01dcc60a7cb8, platform_device_register_full() is > > > available to allocate and register a platform device. > > > > > > If a dma_mask is provided as part of platform_device_info, > > > platform_device_register_full() allocate memory for a u64 using > > > kmalloc(). > > > > > > A comment in the code state that "[t]his memory isn't freed when the > > > device is put". > > > > > > It's never a good thing to leak memory, but there's only very few > > > users of platform_device_info's dma_mask, and those are mostly > > > "static" devices that are not going to be plugged/unplugged often. > > > > > > So memory leak is not really an issue, but allocating 8 bytes through > > > kmalloc() seems overkill. > > > > > > And it's a pity to have to allocate 8 bytes for the dma_mask while up > > > to 7 bytes are wasted at the end of struct platform_object in the form > > > of padding after name field: unfortunately this padding is not used > > > when allocating the memory to hold the name. > > > > > > To address theses issues, this patch adds dma_mask to platform_object > > > struct so that it is always allocated for all struct platform_device > > > allocated through platform_device_alloc() or > > > platform_device_register_full(). > > > And since it's within struct platform_object, dma_mask won't be leaked > > > anymore when struct platform_device got released. Storage for dma_mask > > > is added almost for free by removing the padding at the end of struct > > > platform_object. > How does the padding of name change? The only thing that I see changing > for .name is that it's a char[] now instead of a char[1]. As it was > used as a flexible array already before the padding (which only applies > to a stand alone struct platform_object) doesn't matter. > I guess that is a tool problem that still some padding changes are > reported? > When name is defined as char name[1] at the end of the structure, the compiler is required to add padding after it (since the structure is not "packed" through some compiler extension). This padding is added in order to have a size multiple of the highest required alignement for types insided the structure. This is required so that each item of an array of "struct platform_object" are aligned. Changing name[1] to name[0] or name[] free the compiler from adding storage space for name and thus remove the need for padding after it. > Other than that the patch looks good. > Thanks a lot. -- Yann Droneaud OPTEYA -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCHv4] driver core/platform: don't leak memory allocated for dma_mask
On Fri, Feb 07, 2014 at 03:20:05PM -0800, Greg Kroah-Hartman wrote:
> On Mon, Jan 27, 2014 at 11:05:52AM +0100, Yann Droneaud wrote:
> > Since commit 01dcc60a7cb8, platform_device_register_full() is
> > available to allocate and register a platform device.
> >
> > If a dma_mask is provided as part of platform_device_info,
> > platform_device_register_full() allocate memory for a u64 using
> > kmalloc().
> >
> > A comment in the code state that "[t]his memory isn't freed when the
> > device is put".
> >
> > It's never a good thing to leak memory, but there's only very few
> > users of platform_device_info's dma_mask, and those are mostly
> > "static" devices that are not going to be plugged/unplugged often.
> >
> > So memory leak is not really an issue, but allocating 8 bytes through
> > kmalloc() seems overkill.
> >
> > And it's a pity to have to allocate 8 bytes for the dma_mask while up
> > to 7 bytes are wasted at the end of struct platform_object in the form
> > of padding after name field: unfortunately this padding is not used
> > when allocating the memory to hold the name.
> >
> > To address theses issues, this patch adds dma_mask to platform_object
> > struct so that it is always allocated for all struct platform_device
> > allocated through platform_device_alloc() or
> > platform_device_register_full().
> > And since it's within struct platform_object, dma_mask won't be leaked
> > anymore when struct platform_device got released. Storage for dma_mask
> > is added almost for free by removing the padding at the end of struct
> > platform_object.
How does the padding of name change? The only thing that I see changing
for .name is that it's a char[] now instead of a char[1]. As it was
used as a flexible array already before the padding (which only applies
to a stand alone struct platform_object) doesn't matter.
I guess that is a tool problem that still some padding changes are
reported?
Other than that the patch looks good.
Uwe
> > Padding at the end of the structure is removed by making name a C99
> > flexible array member (eg. a zero sized array). To handle this change,
> > memory allocation is updated to take care of allocating an additional
> > byte for the NUL terminating character.
> >
> > No more memory leak, no small allocation, no byte wasted and
> > a slight reduction in code size.
> >
> > Built on Fedora 20, using GCC 4.8, for ARM, i386, x86_64 and PPC64
> > architectures, the size of the object file and the data structure layout
> > are updated as follow, produced with commands:
> >
> > $ size drivers/base/platform.o
> > $ pahole drivers/base/platform.o \
> >--recursive \
> >--class_name device,pdev_archdata,platform_device,platform_object
> >
> > --- size+pahole.next-20140124
> > +++ size+pahole.next-20140124+
> > @@ -1,5 +1,5 @@
> > textdata bss dec hex filename
> > - 5616 472 32612017e8 obj-arm/drivers/base/platform.o
> > + 5572 472 32607617bc obj-arm/drivers/base/platform.o
> >struct device {
> >struct device *parent; /* 0 4
> > */
> >struct device_private *p;/* 4 4
> > */
> > @@ -77,15 +77,15 @@ struct platform_object {
> >/* XXX last struct has 4 bytes of padding */
> >
> >/* --- cacheline 6 boundary (384 bytes) --- */
> > -char name[1]; /* 384 1
> > */
> > +u64dma_mask; /* 384 8
> > */
> > +char name[0]; /* 392 0
> > */
> >
> > -/* size: 392, cachelines: 7, members: 2 */
> > -/* padding: 7 */
> > +/* size: 392, cachelines: 7, members: 3 */
> >/* paddings: 1, sum paddings: 4 */
> >/* last cacheline: 8 bytes */
> >};
> >
> > textdata bss dec hex filename
> > - 6007 532 32657119ab obj-i386/drivers/base/platform.o
> > + 5943 532 326507196b obj-i386/drivers/base/platform.o
> >struct device {
> >struct device *parent; /* 0 4
> > */
> >struct device_private *p;/* 4 4
> > */
> > @@ -161,14 +161,14 @@ struct platform_device {
> >struct platform_object {
> >struct platform_device pdev; /* 0 392
> > */
> >/* --- cacheline 6 boundary (384 bytes) was 8 bytes ago --- */
> > -char name[1]; /* 392 1
> > */
> > +u64dma_mask; /* 392 8
> > */
> > +char name[0]; /* 400 0
> > */
> >
> > -/* size: 396, cachelines: 7, members: 2 */
> > -/* padding: 3 */
> > -
Re: [PATCHv4] driver core/platform: don't leak memory allocated for dma_mask
On Mon, Jan 27, 2014 at 11:05:52AM +0100, Yann Droneaud wrote:
> Since commit 01dcc60a7cb8, platform_device_register_full() is
> available to allocate and register a platform device.
>
> If a dma_mask is provided as part of platform_device_info,
> platform_device_register_full() allocate memory for a u64 using
> kmalloc().
>
> A comment in the code state that "[t]his memory isn't freed when the
> device is put".
>
> It's never a good thing to leak memory, but there's only very few
> users of platform_device_info's dma_mask, and those are mostly
> "static" devices that are not going to be plugged/unplugged often.
>
> So memory leak is not really an issue, but allocating 8 bytes through
> kmalloc() seems overkill.
>
> And it's a pity to have to allocate 8 bytes for the dma_mask while up
> to 7 bytes are wasted at the end of struct platform_object in the form
> of padding after name field: unfortunately this padding is not used
> when allocating the memory to hold the name.
>
> To address theses issues, this patch adds dma_mask to platform_object
> struct so that it is always allocated for all struct platform_device
> allocated through platform_device_alloc() or platform_device_register_full().
> And since it's within struct platform_object, dma_mask won't be leaked
> anymore when struct platform_device got released. Storage for dma_mask
> is added almost for free by removing the padding at the end of struct
> platform_object.
>
> Padding at the end of the structure is removed by making name a C99
> flexible array member (eg. a zero sized array). To handle this change,
> memory allocation is updated to take care of allocating an additional
> byte for the NUL terminating character.
>
> No more memory leak, no small allocation, no byte wasted and
> a slight reduction in code size.
>
> Built on Fedora 20, using GCC 4.8, for ARM, i386, x86_64 and PPC64
> architectures, the size of the object file and the data structure layout
> are updated as follow, produced with commands:
>
> $ size drivers/base/platform.o
> $ pahole drivers/base/platform.o \
>--recursive \
>--class_name device,pdev_archdata,platform_device,platform_object
>
> --- size+pahole.next-20140124
> +++ size+pahole.next-20140124+
> @@ -1,5 +1,5 @@
> textdata bss dec hex filename
> - 5616 472 32612017e8 obj-arm/drivers/base/platform.o
> + 5572 472 32607617bc obj-arm/drivers/base/platform.o
>struct device {
>struct device *parent; /* 0 4 */
>struct device_private *p;/* 4 4 */
> @@ -77,15 +77,15 @@ struct platform_object {
>/* XXX last struct has 4 bytes of padding */
>
>/* --- cacheline 6 boundary (384 bytes) --- */
> -char name[1]; /* 384 1 */
> +u64dma_mask; /* 384 8 */
> +char name[0]; /* 392 0 */
>
> -/* size: 392, cachelines: 7, members: 2 */
> -/* padding: 7 */
> +/* size: 392, cachelines: 7, members: 3 */
>/* paddings: 1, sum paddings: 4 */
>/* last cacheline: 8 bytes */
>};
>
> textdata bss dec hex filename
> - 6007 532 32657119ab obj-i386/drivers/base/platform.o
> + 5943 532 326507196b obj-i386/drivers/base/platform.o
>struct device {
>struct device *parent; /* 0 4 */
>struct device_private *p;/* 4 4 */
> @@ -161,14 +161,14 @@ struct platform_device {
>struct platform_object {
>struct platform_device pdev; /* 0 392 */
>/* --- cacheline 6 boundary (384 bytes) was 8 bytes ago --- */
> -char name[1]; /* 392 1 */
> +u64dma_mask; /* 392 8 */
> +char name[0]; /* 400 0 */
>
> -/* size: 396, cachelines: 7, members: 2 */
> -/* padding: 3 */
> -/* last cacheline: 12 bytes */
> +/* size: 400, cachelines: 7, members: 3 */
> +/* last cacheline: 16 bytes */
>};
>
> textdata bss dec hex filename
> - 88512112 48 110112b03 obj-ppc64/drivers/base/platform.o
> + 87872104 48 109392abb obj-ppc64/drivers/base/platform.o
>struct device {
>struct device *parent; /* 0 8 */
>struct device_private *p;/* 8 8 */
> @@ -256,14 +256,14 @@ struct platform_device {
>struct platform_object {
>struct platform_device pdev; /*
[PATCHv4] driver core/platform: don't leak memory allocated for dma_mask
Since commit 01dcc60a7cb8, platform_device_register_full() is
available to allocate and register a platform device.
If a dma_mask is provided as part of platform_device_info,
platform_device_register_full() allocate memory for a u64 using
kmalloc().
A comment in the code state that "[t]his memory isn't freed when the
device is put".
It's never a good thing to leak memory, but there's only very few
users of platform_device_info's dma_mask, and those are mostly
"static" devices that are not going to be plugged/unplugged often.
So memory leak is not really an issue, but allocating 8 bytes through
kmalloc() seems overkill.
And it's a pity to have to allocate 8 bytes for the dma_mask while up
to 7 bytes are wasted at the end of struct platform_object in the form
of padding after name field: unfortunately this padding is not used
when allocating the memory to hold the name.
To address theses issues, this patch adds dma_mask to platform_object
struct so that it is always allocated for all struct platform_device
allocated through platform_device_alloc() or platform_device_register_full().
And since it's within struct platform_object, dma_mask won't be leaked
anymore when struct platform_device got released. Storage for dma_mask
is added almost for free by removing the padding at the end of struct
platform_object.
Padding at the end of the structure is removed by making name a C99
flexible array member (eg. a zero sized array). To handle this change,
memory allocation is updated to take care of allocating an additional
byte for the NUL terminating character.
No more memory leak, no small allocation, no byte wasted and
a slight reduction in code size.
Built on Fedora 20, using GCC 4.8, for ARM, i386, x86_64 and PPC64
architectures, the size of the object file and the data structure layout
are updated as follow, produced with commands:
$ size drivers/base/platform.o
$ pahole drivers/base/platform.o \
--recursive \
--class_name device,pdev_archdata,platform_device,platform_object
--- size+pahole.next-20140124
+++ size+pahole.next-20140124+
@@ -1,5 +1,5 @@
textdata bss dec hex filename
- 5616 472 32612017e8 obj-arm/drivers/base/platform.o
+ 5572 472 32607617bc obj-arm/drivers/base/platform.o
struct device {
struct device *parent; /* 0 4 */
struct device_private *p;/* 4 4 */
@@ -77,15 +77,15 @@ struct platform_object {
/* XXX last struct has 4 bytes of padding */
/* --- cacheline 6 boundary (384 bytes) --- */
-char name[1]; /* 384 1 */
+u64dma_mask; /* 384 8 */
+char name[0]; /* 392 0 */
-/* size: 392, cachelines: 7, members: 2 */
-/* padding: 7 */
+/* size: 392, cachelines: 7, members: 3 */
/* paddings: 1, sum paddings: 4 */
/* last cacheline: 8 bytes */
};
textdata bss dec hex filename
- 6007 532 32657119ab obj-i386/drivers/base/platform.o
+ 5943 532 326507196b obj-i386/drivers/base/platform.o
struct device {
struct device *parent; /* 0 4 */
struct device_private *p;/* 4 4 */
@@ -161,14 +161,14 @@ struct platform_device {
struct platform_object {
struct platform_device pdev; /* 0 392 */
/* --- cacheline 6 boundary (384 bytes) was 8 bytes ago --- */
-char name[1]; /* 392 1 */
+u64dma_mask; /* 392 8 */
+char name[0]; /* 400 0 */
-/* size: 396, cachelines: 7, members: 2 */
-/* padding: 3 */
-/* last cacheline: 12 bytes */
+/* size: 400, cachelines: 7, members: 3 */
+/* last cacheline: 16 bytes */
};
textdata bss dec hex filename
- 88512112 48 110112b03 obj-ppc64/drivers/base/platform.o
+ 87872104 48 109392abb obj-ppc64/drivers/base/platform.o
struct device {
struct device *parent; /* 0 8 */
struct device_private *p;/* 8 8 */
@@ -256,14 +256,14 @@ struct platform_device {
struct platform_object {
struct platform_device pdev; /* 0 728 */
/* --- cacheline 11 boundary (704 bytes) was 24 bytes ago --- */
-char name[1]; /* 728 1 */
+u64dma_mask; /* 728 8 */
+char
