On Tue, May 12, 2026 at 10:02:04AM -0700, Darrick J. Wong wrote: > OH. Now I remember why -- it's to handle contiguous mixed mappings > better. > > Let's say that you have a 1k fsblock filesystem and 4k base pages. You > fallocate an 8G swap file and then mkswap it. The first mapping is a 1k > written mapping at offset 0 for the swap header, followed by an 8388607k > unwritten mapping at offset 3k. > > The PAGE_SIZE rounding code in iomap_swapfile_add_extent will round the > end of that first mapping down to zero and ignore it. The second > mapping will be treated as if it were a 8388604k mapping starting at > offset 4096. Now the page counts are wrong and the swapon fails.
Do we care about this use case? I guess you did as you implemented his, but still? > > A more generic solution to this would be to change add_swap_extent to > take sector_t addr and length values and use them to construct a bitmap > representing contiguous physical space on the bdev, accounting of course > for PAGE_SIZE alignment. Except for the swap header page, every other > contiguously set page-aligned region in the bitmap gets added to the > swap extent map. You don't even need a bitmap, just do basically the same checks as the iomap code when moving to a new swap extent after moving to use the sector_t. And it really should anyway, as the current abuse of sector_t to store a disk offset in PAGE_SIZE units is pretty gross. _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
