Hi Dave, On 09/23/2013 08:56 AM, Dave Chinner wrote: > On Sun, Sep 22, 2013 at 04:25:15PM +0800, Jeff Liu wrote: >> From: Jie Liu <jeff.liu@xxxxxxxxxx> >> >> At xfs_iext_realloc_direct(), the new_size is changed by adding >> if_bytes if originally the extent records are stored at the inline >> extent buffer, and we have to switch from it to a direct extent >> list for those new allocated extents, this is wrong. e.g, >> >> Create a file with three extents which was showing as following, >> >> xfs_io -f -c "truncate 100m" /xfs/testme >> >> for i in $(seq 0 5 10); do >> offset=$(($i * $((1 << 20)))) >> xfs_io -c "pwrite $offset 1m" /xfs/testme >> done >> >> Inline >> ------ >> irec: if_bytes bytes_diff new_size >> 1st 0 16 16 >> 2nd 16 16 32 >> >> Switching >> --------- rnew_size >> 3rd 32 16 48 + 32 = 80 roundup=128 >> >> In this case, the desired value of new_size should be 48, and then >> it will be roundup to 64 and be assigned to rnew_size. > > Ok, so it allocates 128 bytes instead of 64 bytes. It tracks that > allocation size correctly ifp->if_real_bytes, and all it means is > that there are 4 empty extra slots in the extent array. The code > already handles having empty slots in the direct extent array, so > what impact is there as a result of the oversized initial allocation > that is currently happening? > > i.e. if fixing the oversized results in more memory allocations due > to resizing more regularly, then is there a benefit to changing this > code given that the rewrite of the ifp->if_bytes value in the case > where we do inline->direct conversion prevents this over-allocation > from being a problem... I guess my current patch subject/description mislead you. The result of the oversized can be ignored since this can be handled in the direct extent array as empty slots. Actually, what I want to say is that we don't need to perform "new_size += ifp->if_bytes;" again at xfs_iext_realloc_direct() because the new_size at xfs_iext_add() already be the size of extents after adding, just as the variable comments is mentioned. Thanks, -Jeff _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
