Messages in this thread | | | Date | Tue, 12 Dec 2023 07:46:51 +0000 | Subject | Re: [RFC 0/7] ext4: Allocator changes for atomic write support with DIO | From | John Garry <> |
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On 11/12/2023 10:54, Ojaswin Mujoo wrote: >> This seems a rather big drawback. > So if I'm not wrong, we force the extent alignment as well as the size > of the extent in xfs right.
For XFS in my v1 patchset, we only force alignment (but not size).
It is assumed that the user will fallocate/dd the complete file before issuing atomic writes, and we will have extent alignment and length as required.
However - as we have seen with a trial user - it can create a problem if we don't do that and we write 4K and then overwrite with a 16K atomic write to a file, as 2x extents may be allocated for the complete 16K and it cannot be issued as a single BIO.
> > We didn't want to overly restrict the users of atomic writes by forcing > the extents to be of a certain alignment/size irrespective of the size > of write. The design in this patchset provides this flexibility at the > cost of some added precautions that the user should take (eg not doing > an atomic write on a pre existing unaligned extent etc).
Doesn't bigalloc already give you what you require here?
Thanks, John
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