From e47f1f56dd82cc6d91f5c4d914a534aa03cd12ca Mon Sep 17 00:00:00 2001 From: Brendan Jackman Date: Fri, 28 Feb 2025 09:52:17 +0000 Subject: mm/page_alloc: clarify terminology in migratetype fallback code Patch series "mm/page_alloc: Some clarifications for migratetype fallback", v4. A couple of patches to try and make the code easier to follow. This patch (of 2): This code is rather confusing because: 1. "Steal" is sometimes used to refer to the general concept of allocating from a from a block of a fallback migratetype (steal_suitable_fallback()) but sometimes it refers specifically to converting a whole block's migratetype (can_steal_fallback()). 2. can_steal_fallback() sounds as though it's answering the question "am I functionally permitted to allocate from that other type" but in fact it is encoding a heuristic preference. 3. The same piece of data has different names in different places: can_steal vs whole_block. This reinforces point 2 because it looks like the different names reflect a shift in intent from "am I allowed to steal" to "do I want to steal", but no such shift exists. Fix 1. by avoiding the term "steal" in ambiguous contexts. Start using the term "claim" to refer to the special case of stealing the entire block. Fix 2. by using "should" instead of "can", and also rename its parameters and add some commentary to make it more explicit what they mean. Fix 3. by adopting the new "claim" terminology universally for this set of variables. Link: https://lkml.kernel.org/r/20250228-clarify-steal-v4-0-cb2ef1a4e610@google.com Link: https://lkml.kernel.org/r/20250228-clarify-steal-v4-1-cb2ef1a4e610@google.com Signed-off-by: Brendan Jackman Reviewed-by: Vlastimil Babka Cc: Johannes Weiner Cc: Mel Gorman Cc: Michal Hocko Cc: Yosry Ahmed Signed-off-by: Andrew Morton --- mm/compaction.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'mm/compaction.c') diff --git a/mm/compaction.c b/mm/compaction.c index a3203d97123e..2e2d4db33e68 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -2332,7 +2332,7 @@ static enum compact_result __compact_finished(struct compact_control *cc) ret = COMPACT_NO_SUITABLE_PAGE; for (order = cc->order; order < NR_PAGE_ORDERS; order++) { struct free_area *area = &cc->zone->free_area[order]; - bool can_steal; + bool claim_block; /* Job done if page is free of the right migratetype */ if (!free_area_empty(area, migratetype)) @@ -2349,7 +2349,7 @@ static enum compact_result __compact_finished(struct compact_control *cc) * other migratetype buddy lists. */ if (find_suitable_fallback(area, order, migratetype, - true, &can_steal) != -1) + true, &claim_block) != -1) /* * Movable pages are OK in any pageblock. If we are * stealing for a non-movable allocation, make sure -- cgit v1.2.3