On ma, 2016-04-04 at 14:18 +0100, Chris Wilson wrote: > From: Akash Goel <akash.goel@xxxxxxxxx> > > On a long run of more than 2-3 days, physical memory tends to get > fragmented severely, which considerably slows down the system. In such a > scenario, the shrinker is also unable to help as lack of memory is not > the actual problem, since it has been observed that there are enough free > pages of 0 order. This also manifests itself when an indiviual zone in > the mm runs out of pages and if we cannot migrate pages between zones, > the kernel hits an out-of-memory even though there are free pages (and > often all of swap) available. > > To address the issue of external fragementation, kernel does a compaction > (which involves migration of pages) but it's efficacy depends upon how > many pages are marked as MOVABLE, as only those pages can be migrated. > > Currently the backing pages for GFX buffers are allocated from shmemfs > with GFP_RECLAIMABLE flag, in units of 4KB pages. In the case of limited > swap space, it may not be possible always to reclaim or swap-out pages of > all the inactive objects, to make way for free space allowing formation > of higher order groups of physically-contiguous pages on compaction. > > Just marking the GPU pages as MOVABLE will not suffice, as i915.ko has to > pin the pages if they are in use by GPU, which will prevent their > migration. So the migratepage callback in shmem is also hooked up to get > a notification when kernel initiates the page migration. On the > notification, i915.ko appropriately unpin the pages. With this we can > effectively mark the GPU pages as MOVABLE and hence mitigate the > fragmentation problem. > > v2: > - Rename the migration routine to gem_shrink_migratepage, move it to the > shrinker file, and use the existing constructs (Chris) > - To cleanup, add a new helper function to encapsulate all page migration > skip conditions (Chris) > - Add a new local helper function in shrinker file, for dropping the > backing pages, and call the same from gem_shrink() also (Chris) > > v3: > - Fix/invert the check on the return value of unsafe_drop_pages (Chris) > > v4: > - Minor tidy > > Testcase: igt/gem_shrink > Bugzilla: (e.g.) https://bugs.freedesktop.org/show_bug.cgi?id=90254 > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Signed-off-by: Sourab Gupta <sourab.gupta@xxxxxxxxx> > Signed-off-by: Akash Goel <akash.goel@xxxxxxxxx> > Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Could this patch be re-spinned on top of current nightly? After removing; > WARN(page_count(newpage) != 1, "Unexpected ref count for newpage\n") and > if (ret) > DRM_DEBUG_DRIVER("page=%p migration returned %d\n", page, ret); This is; Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> Regards, Joonas -- Joonas Lahtinen Open Source Technology Center Intel Corporation -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>