Commits on Aug 14, 2024

1. fs/ufs: change default locking protocol …

   The fs/ufs component by default disabled all file locking before
   read/write operations (except for NFS file systems). This was based on
   the assumption, that the file system itself performs the required
   locking operation and hence we don't have to add to it.
   
   This assumption is incorrect when using data sieving. In data sieving,
   the code 'ignore' small gaps when we write to a file, and perform
   instead a read-modify-write sequence ourselves for performance reasons.
   The problem is however that even within a collective operation not all
   aggregators might want to use data sieving. Hence, enabling locking just
   for the data-sieving routines is insufficient, all processes have to
   perform the locking. Therefore, our two options are: a) either disable
   write data-sieving by default, or b) enable range-locking by default.
   
   After some testing, I think enabling range-locking be default is the
   safer and better approach. It doesn't seem to show any significant
   performance impact on my test systems.
   
   Note, that on Lustre file systems, we can keep the default to no-locking
   as far as I can see, since the collective algorithm used by Lustre is
   unlikely to produce this pattern. I did add in however an mca parameter
   that allows us to control the locking algorithm used by the Lustre
   component as well, in case we need to change that for a particular
   use-case or platform.
   
   Fixes Issue open-mpi#12718
   
   Signed-off-by: Edgar Gabriel <[email protected]>
   (cherry picked from commit c697f28)

   

   edgargabriel committed Aug 14, 2024
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