Jonathan Adams wrote:
> [ snipped...]
>
> Looking at the ::kmem_cache output:
>
> 32-bit:
> >::kmem_cache ! grep streams_dblk_1984
> cac2e2b0 streams_dblk_1984 020f 00 2048 9
>
> 64-bit
> > ::kmem_cache ! grep streams_dblk_1936
> ec0033c08 streams_dblk_1936 0269 00 2048 602
>
> The third field is the "flags" field; this contains the full reason
> for all the differences you noticed.
>
> 32-bit: KMF_HASH | KMF_CONTENTS | KMF_AUDIT | KMF_DEADBEEF | KMF_REDZONE
> 64-bit: KMF_HASH | KMF_CONTENTS | KMF_AUDIT | KMF_FIREWALL |
> KMF_NOMAGAZINE
>
> The flags they both have are KMF_HASH (buffers require a hash table to
> track control structures), KMF_CONTENTS (record contents of buffer
> upon free), KMF_AUDIT (record information about each allocation and
> free).
>
> The 64-bit cache is a firewall cache; this means the buffer size is
> rounded up to a multiple of PAGESIZE, and all buffers are allocated so
> that the end of the buffer is at the end of a page. The allocation is
> then done in such a way that there is an unmapped VA hole *after* that
> page, and so that allocation addresses are not re-used recently. The
> magazine (that is, caching) layer of the cache is disabled, which
> means that the objects are freed and unmapped immediately upon
> kmem_cache_free().
>
> The 32-bit cache is a standard debugging cache; the slabs are five
> pages long, which is 9 buffers / slab (0x5000 / 0x540); the extra 40
> bytes is a "REDZONE", used to detect buffer overruns, etc. The
> magazine layer is *enabled*, which means that freed buffers are
> cached, until the system notices that we're running low on space.
>
> The difference only exists on DEBUG kernels, and is because
> firewalling is not done on 32-bit platforms, since the allocation
> patterns used waste and fragment VA space.
>
> On a non-debug system, the setup will be pretty much the same between
> 32-bit and 64-bit systems.
>
Hi Jonathan,
I have a question about your comments above:
Raymond have told me he already set the kmem_flags = 0xf in the system,
why the kmem cache debug flags are still different between 32bit and
64bit kernel?
The kmem_flags setting should be effecting for all of cache, right?
Anyway, thanks for your reply, I do learn something from it. :-)
--
Cheers,
--
Oliver Yang | Work from home | http://blog.csdn.net/yayong
