nux distro kernel.</subtitle>
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<updated>2024-09-02T14:53:53Z</updated>
<entry>
<title>dm: Make use of __assign_bit() API</title>
<updated>2024-09-02T14:53:53Z</updated>
<author>
<name>Hongbo Li</name>
<email>lihongbo22@huawei.com</email>
</author>
<published>2024-09-02T13:11:23Z</published>
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<content type='text'>
We have for some time the __assign_bit() API to replace
open coded
    if (foo)
        __set_bit(n, bar);
    else
        __clear_bit(n, bar);

Use this API to simplify the code. No functional change
intended.

Signed-off-by: Hongbo Li &lt;lihongbo22@huawei.com&gt;
Signed-off-by: Mikulas Patocka &lt;mpatocka@redhat.com&gt;
</content>
</entry>
<entry>
<title>dm: Constify struct dm_block_validator</title>
<updated>2024-07-19T10:08:15Z</updated>
<author>
<name>Christophe JAILLET</name>
<email>christophe.jaillet@wanadoo.fr</email>
</author>
<published>2024-07-14T07:13:56Z</published>
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<content type='text'>
'struct dm_block_validator' are not modified in these drivers.

Constifying this structure moves some data to a read-only section, so
increase overall security.

On a x86_64, with allmodconfig, as an example:

Before:
======
   text	   data	    bss	    dec	    hex	filename
  32047	    920	     16	  32983	   80d7	drivers/md/dm-cache-metadata.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  32075	    896	     16	  32987	   80db	drivers/md/dm-cache-metadata.o

Signed-off-by: Christophe JAILLET &lt;christophe.jaillet@wanadoo.fr&gt;
Signed-off-by: Mikulas Patocka &lt;mpatocka@redhat.com&gt;
</content>
</entry>
<entry>
<title>bitmap: introduce generic optimized bitmap_size()</title>
<updated>2024-04-01T09:49:28Z</updated>
<author>
<name>Alexander Lobakin</name>
<email>aleksander.lobakin@intel.com</email>
</author>
<published>2024-03-27T15:23:49Z</published>
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<id>urn:sha1:a37fbe666c016fd89e4460d0ebfcea05baba46dc</id>
<content type='text'>
The number of times yet another open coded
`BITS_TO_LONGS(nbits) * sizeof(long)` can be spotted is huge.
Some generic helper is long overdue.

Add one, bitmap_size(), but with one detail.
BITS_TO_LONGS() uses DIV_ROUND_UP(). The latter works well when both
divident and divisor are compile-time constants or when the divisor
is not a pow-of-2. When it is however, the compilers sometimes tend
to generate suboptimal code (GCC 13):

48 83 c0 3f          	add    $0x3f,%rax
48 c1 e8 06          	shr    $0x6,%rax
48 8d 14 c5 00 00 00 00	lea    0x0(,%rax,8),%rdx

%BITS_PER_LONG is always a pow-2 (either 32 or 64), but GCC still does
full division of `nbits + 63` by it and then multiplication by 8.
Instead of BITS_TO_LONGS(), use ALIGN() and then divide by 8. GCC:

8d 50 3f             	lea    0x3f(%rax),%edx
c1 ea 03             	shr    $0x3,%edx
81 e2 f8 ff ff 1f    	and    $0x1ffffff8,%edx

Now it shifts `nbits + 63` by 3 positions (IOW performs fast division
by 8) and then masks bits[2:0]. bloat-o-meter:

add/remove: 0/0 grow/shrink: 20/133 up/down: 156/-773 (-617)

Clang does it better and generates the same code before/after starting
from -O1, except that with the ALIGN() approach it uses %edx and thus
still saves some bytes:

add/remove: 0/0 grow/shrink: 9/133 up/down: 18/-538 (-520)

Note that we can't expand DIV_ROUND_UP() by adding a check and using
this approach there, as it's used in array declarations where
expressions are not allowed.
Add this helper to tools/ as well.

Reviewed-by: Przemek Kitszel &lt;przemyslaw.kitszel@intel.com&gt;
Acked-by: Yury Norov &lt;yury.norov@gmail.com&gt;
Signed-off-by: Alexander Lobakin &lt;aleksander.lobakin@intel.com&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;
</content>
</entry>