From: Zhou Wenjian <zhouwj-fnst@xxxxxxxxxxxxxx>
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
>
>
> _______________________________________________
> kexec mailing list
> kexec at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
--
Thanks.
HATAYAMA, Daisuke
