Re: [PATCH v3 2/3] ext4: correct the judgment of BUG in ext4_mb_normalize_request

[Baokun Li]

在 2022/5/28 23:12, Ritesh Harjani 写道:
> On 22/05/28 07:00PM, Baokun Li wrote:
> > ext4_mb_normalize_request() can move logical start of allocated blocks
> > to reduce fragmentation and better utilize preallocation. However logical
> > block requested as a start of allocation (ac->ac_o_ex.fe_logical) should
> > always be covered by allocated blocks so we should check that by
> > modifying and to or in the assertion.
> >
> > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> Changes looks good to me as we discussed. Feel free to add -
>
> Reviewed-by: Ritesh Harjani <ritesh.list@xxxxxxxxx>
>
> > ---
> > V1->V2:
> > 	Change Fixes from dfe076c106f6 to c9de560ded61.
> > V2->V3:
> > 	Delete Fixes tag.
> > 	Add more comments and commit logs to make the code easier to understand.
> >
> >   fs/ext4/mballoc.c | 17 ++++++++++++++++-
> >   1 file changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index 4d3740fdff90..9e06334771a3 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -4185,7 +4185,22 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
> >   	}
> >   	rcu_read_unlock();
> >
> > -	if (start + size <= ac->ac_o_ex.fe_logical &&
> > +	/*
> > +	 * In this function "start" and "size" are normalized for better
> > +	 * alignment and length such that we could preallocate more blocks.
> > +	 * This normalization is done such that original request of
> > +	 * ac->ac_o_ex.fe_logical & fe_len should always lie within "start" and
> > +	 * "size" boundaries.
> > +	 * (Note fe_len can be relaxed since FS block allocation API does not
> > +	 * provide gurantee on number of contiguous blocks allocation since that
> > +	 * depends upon free space left, etc).
> > +	 * In case of inode pa, later we use the allocated blocks
> > +	 * [pa_start + fe_logical - pa_lstart, fe_len/size] from the preallocated
> > +	 * range of goal/best blocks [start, size] to put it at the
> > +	 * ac_o_ex.fe_logical extent of this inode.
> > +	 * (See ext4_mb_use_inode_pa() for more details)
> > +	 */
> > +	if (start + size <= ac->ac_o_ex.fe_logical ||
> >   			start > ac->ac_o_ex.fe_logical) {
> >   		ext4_msg(ac->ac_sb, KERN_ERR,
> >   			 "start %lu, size %lu, fe_logical %lu",
> > --
> > 2.31.1
> .

Thank you for your review!
--
With Best Regards,
Baokun Li