Re: Disk Cache Patch

"Changju Gao" <[email protected]> wrote on 06/12/2007 12:57:54 PM:

> Here is how the same address is used.
>
> In LD_discover(), a local variable "working_disk" is used
> (repeatedly) to create new
> objects from a list of devices.
>
> Then, get_geometry() is called, which in turn calls
> get_partition_table_geometry(),
> which calls LD_read(), which calls read_from_cache(). If no hit in
> read_from_cache(),
> write_to_cache() will be called (afer a successful write).
>
> So the cache entries are identified by the address of
> "working_disk", which is the same
> in consecutive calls inside LD_discover().
>
>
> According to the log file, here is the when entries are created:
>
> grep -n "Create a new cache entry for disk " evms-engine.2.log | head -3
>
> 10216:Jun 05 16:30:42 lab104 _8_ LocalDskMgr: write_to_cache: Create
> a new cache entry for disk cciss!c0d0, sector 0, count 1.
> 14314:Jun 05 16:30:42 lab104 _8_ LocalDskMgr: write_to_cache: Create
> a new cache entry for disk cciss/c0d0, sector 0, count 2.
> 14378:Jun 05 16:30:42 lab104 _8_ LocalDskMgr: write_to_cache: Create
> a new cache entry for disk cciss/c0d1, sector 0, count 2.
>
> When entries are hit:
>
> grep -n "read_from_cache: Read from cache." evms-engine.2.log | head -3
>
> 10371:Jun 05 16:30:42 lab104 _8_ LocalDskMgr: read_from_cache: Read
> from cache.  disk cciss!c0d1, sector 0, count 1.
> 10529:Jun 05 16:30:42 lab104 _8_ LocalDskMgr: read_from_cache: Read
> from cache.  disk cciss!c0d2, sector 0, count 1.
> 10691:Jun 05 16:30:42 lab104 _8_ LocalDskMgr: read_from_cache: Read
> from cache.  disk cciss!c0d3, sector 0, count 1.
>
>
> Even though the addresses are not printed in the log, you can
> clearly see we hit
> disk "cciss!c0d1" in the cache at line 10371. Disk "cciss!c0d1" was never
put
> in the cache. Even disk "cciss/c0d1" was put in AFTER the bogus hit.
>
>
> Hope this clear things up.
>
>
> Best regards,
>
>
> - Changju

Thanks for the explanation.  And thanks again for the patch.

I finally got around to checking the fix into CVS and posting the patch on
the EVMS home page:  http://evms.sourceforge.net/patches/2.5.5
/engine/disk_cache.patch

Steve D.

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