[PATCH v1 0/4] makedumpfile: optimize the way of generating incomplete kdump core

[HATAYAMA Daisuke]

From: Zhou Wenjian <zhouwj-fnst at cn.fujitsu.com>
Subject: [PATCH v1 0/4] makedumpfile: optimize the way of generating incomplete kdump core
Date: Fri, 10 Jul 2015 10:28:49 +0800

I don't think this subject is good. This seems a bugfix patch set for
ENOSPC issue, not an optimization.

> 
> In current implementation, when generating kdump core,
> it behaves as the following logic.
> 
> 1. Write page header into the buffer cd_header.
> 2. If buffer is full, flush the buffer.
> 3. Write page data into the buffer cd_page.
> 4. If buffer is full, flush the buffer.
> 
> When enospc occurs in flushing cd_page, it always still
> has much data in cd_header. The size of page data is 170
> times the size of page header. It leads to that quite a
> lot of page data been written into file can't be used.
> 

Do you mean like this?

  When ENOSPC occurs in flushing cd_page, there's still data left in
  cd_header. We cannot read page data corresponding to the page
  headers in the cd_header even if the page data has been flushed into
  disk. The size of page data is 170 times larger than the size of
  page header per a single page frame. The difference becomes bigger
  if we use compression.

> The page header may also meet that. The page data can be
> compressed, so the size of page data can also be much smaller
> than the size of page header.
> 

Compression doesn't always reduce size of data. So writing this
doesn't make sense in general because.

> This patch set changes the logic of generating kdump core.
> The new logic is:

The below doesn't explain why this new logic makes sense.

> 
> 1. Before writing page header and data into buffer, if the buffer
>    will be full, write the data of the buffer into file.

                             This "the buffer" means cd_page, right?

> 2. Then, write the page header and data info buffer.

It's better to write cd_header and cd_page for clarity. "the buffer"
seems ambiguous.

> 
> When enospc occurs in writing the cd_header into file, fill the
> cd_header with zero and re-write the cd_header.
> When enospc occurs in writing the cd_page into file, fill part
> of the cd_header with zero according to how many pages in cd_page
> have been written. 
> 

> Zhou Wenjian (4):
>   Add write_cd_buf
>   Add get_pfn_offset
>   Add write_kdump_page
>   Use write_kdump_page instead of write_cache in
>     write_kdump_pages_cyclic
> 
>  makedumpfile.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 96 insertions(+), 11 deletions(-)
> 
> -- 
> 1.8.3.1
> 
> 
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--
Thanks.
HATAYAMA, Daisuke