Re: [PATCH v2] printk: Improve memory usage logging during boot
From: Petr Mladek
Date: Tue Oct 01 2024 - 11:46:57 EST
On Mon 2024-09-30 11:48:24, Isaac J. Manjarres wrote:
> When the initial printk ring buffer size is updated, setup_log_buf()
> allocates a new ring buffer, as well as a set of meta-data structures
> for the new ring buffer. The function also emits the new size of the
> ring buffer, but not the size of the meta-data structures.
>
> This makes it difficult to assess how changing the log buffer size
> impacts memory usage during boot.
>
> For instance, increasing the ring buffer size from 512 KB to 1 MB
> through the command line yields an increase of 2304 KB in reserved
> memory at boot, while the only obvious change is the 512 KB
> difference in the ring buffer sizes:
>
> log_buf_len=512K:
>
> printk: log_buf_len: 524288 bytes
> Memory: ... (... 733252K reserved ...)
>
> log_buf_len=1M:
>
> printk: log_buf_len: 1048576 bytes
> Memory: ... (... 735556K reserved ...)
>
> This is because of how the size of the meta-data structures scale with
> the size of the ring buffer.
>
> Even when there aren't changes to the printk ring buffer size (i.e. the
> initial size == 1 << CONFIG_LOG_BUF_SHIFT), it is impossible to tell
> how much memory is consumed by the printk ring buffer during boot.
>
> Therefore, unconditionally log the sizes of the printk ring buffer
> and its meta-data structures, so that it's easier to understand
> how changing the log buffer size (either through the command line or
> by changing CONFIG_LOG_BUF_SHIFT) affects boot time memory usage.
>
> With the new logs, it is much easier to see exactly why the memory
> increased by 2304 KB:
>
> log_buf_len=512K:
>
> printk: log_buf_len: 524288 bytes
> printk: prb_descs size: 393216 bytes
> printk: printk_infos size: 1441792 bytes
This should get updated to the new format.
If I count correctly then it should be:
printk: log buffer data + meta data: 524288 + 1835008 = 2359296 bytes
> Memory: ... (... 733252K reserved ...)
>
> log_buf_len=1M:
>
> printk: log_buf_len: 1048576 bytes
> printk: prb_descs size: 786432 bytes
> printk: printk_infos size: 2883584 bytes
and here:
printk: log buffer data + meta data: 1048576 + 3670016 = 4718592 bytes
> Memory: ... (... 735556K reserved ...)
>
> Signed-off-by: Isaac J. Manjarres <isaacmanjarres@xxxxxxxxxx>
Otherwise, it looks good. With the updated commit message:
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Tested-by: Petr Mladek <pmladek@xxxxxxxx>
Note need to send v3. I could update the commit message when committing
the patch.
I am going to wait few days for a potential another review
before pushing.
Best Regards,
Petr