Re: [PATCH] xfs: make xfs_log_iovec independent from xfs_log_vec and release it early

[Christoph Hellwig <hch@infradead.org>]

On Tue, Jun 25, 2024 at 12:06:14AM +0800, Jinliang Zheng wrote:
> xfs_log_iovec is where all log data is saved. Compared to xfs_log_vec itself,
> xfs_log_iovec occupies a larger memory space.
> 
> When their memory spaces are allocated together, the memory occupied by
> xfs_log_iovec can only be released after iclog is written to the disk log
> space. But when xfs_log_iovec is written to iclog, its existence becomes
> meaningless, because a copy of its content is already saved in iclog at this
> time.
> 
> And if they are separated, we can release its memory when the data in
> xfs_log_iovec is written to iclog. The interval between these two time points
> is not too small.
> 
> Since xfs_log_iovec is the area that currently uses the most memory in
> xfs_log_vec, this means that we have released quite a lot of memory. Freeing
> memory that occupies a larger size earlier means smaller memory usage.

This all needs to go into the commit log.  Preferably including the
actual quantity of memory saved for a useful workload.