bug#60474: 30.0.50; `write-region-inhibit-fsync' and copy-on-write file systems

[Paul Eggert]

On 2023-01-02 04:12, Eli Zaretskii wrote:
> Thanks, this is okay for master, but could you perhaps add a sentence,
> in the manual and in NEWS, about the exceptional situations when this
> variable should be reset to nil?  I think we should say something,
> otherwise the need for the variable is questionable.

I gave that a shot and installed the attached patch to master. This 
patch also removes a now-duplicate assignment to 
write_region_inhibit_fsync in init_fileio. Closing the bug report.

While doing this I noticed that the only place 
write-region-inhibit-fsync is let-bound to nil in Emacs's own code is in 
lisp/emacs-lisp/multisession.el, due to commit 
ccb602836426f1fc2e43fa3506427744668f24c6 dated 2021-12-17 which I 
hypothesize is due to MS-Windows needing it when multiple processes are 
accessing the same file in a transaction-like application. So the 
attached patch adds some wording to that effect. Please feel free to 
improve it. I suppose for similar reasons it may also be helpful in 
GNU/Linux with transaction-like Emacs apps on networked file systems; I 
haven't checked this, though, and anyway once you're on a network this 
sort of thing is dubious anyway.

0001-Improve-interactive-file-saving-performance.patch
Description: Text Data