On Wed, May 07 2014, Andrew Morton <[email protected]> wrote:
> On Tue, 6 May 2014 19:22:43 -0700 (PDT) David Rientjes <[email protected]> > wrote: > >> Memory compaction works by having a "freeing scanner" scan from one end of a >> zone which isolates pages as migration targets while another "migrating >> scanner" >> scans from the other end of the same zone which isolates pages for migration. >> >> When page migration fails for an isolated page, the target page is returned >> to >> the system rather than the freelist built by the freeing scanner. This may >> require the freeing scanner to continue scanning memory after suitable >> migration >> targets have already been returned to the system needlessly. >> >> This patch returns destination pages to the freeing scanner freelist when >> page >> migration fails. This prevents unnecessary work done by the freeing scanner >> but >> also encourages memory to be as compacted as possible at the end of the zone. >> >> Reported-by: Greg Thelen <[email protected]> > > What did Greg actually report? IOW, what if any observable problem is > being fixed here? I detected the problem at runtime seeing that ext4 metadata pages (esp the ones read by "sbi->s_group_desc[i] = sb_bread(sb, block)") were constantly visited by compaction calls of migrate_pages(). These pages had a non-zero b_count which caused fallback_migrate_page() -> try_to_release_page() -> try_to_free_buffers() to fail. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
