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Subject: Re: Ideas how to improve Cygwin /usr/bin/find, rm -Rf etc.
 performance...
To: cygwin AT cygwin DOT com
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Date: Thu, 5 Mar 2026 07:37:17 +0100
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From: Jakob Bohm via Cygwin <cygwin AT cygwin DOT com>
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On 02/03/2026 23:42, Roland Mainz via Cygwin wrote:
> Hi!
>
> ----
>
> Quick note (mainly for Corinna):
> Cygwin 3.7.0, I noticed a possible performance improvement while
> working on ms-nfs41-client:
> For each file/dir listed by /usr/bin/find, rm -Rf .. etc I see two
> QueryVolumeInformation (volumequery class=1 and class=4) which
> technically could be cached per mount+process.
>
> I also recall an old confcall at SUN around |openat(dirfd, ...)|,
> technically this info could also be cached per-dirfd (and inherited if
> the dirfd is used to |openat()| another dir fd), making such a cache
> last longer...
The hard part of this is to quickly (without slowing down the total)
detect if a subdirectory is a mountpoint for some other location
(possibly within the same file system, yes windows has had the equivalent
of bind mounts ever since the MSDOS added the JOIN command).

Similarly, find --xdev etc. should stop at such subdir mounts that don't
change st_dev (kernel/cygwin1 changes that assign virtual IDs to each bind
mount don't work as they would hurt other uses of st_dev).

A more practical way until POSIX agrees on a solution is for cygwin to
keep an in-process cache per "volume serial number" from the
GetFileInformaionByHandle() equivalant of fstat()


Enjoy

Jakob
-- 
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
Transformervej 29, 2860 Søborg, Denmark.  Direct +45 31 13 16 10
This public discussion message is non-binding and may contain errors.
WiseMo - Remote Service Management for PCs, Phones and Embedded


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