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Therefore, switch to a more > explicit/verbose style that encodes the status and migratetype > separately. > > In the spirit of making things more explicit, also create an enum to > avoid using magic integer literals with special meanings. This enables > documenting the values at their definition instead of in one of the > callers. > > Signed-off-by: Brendan Jackman Seems independent patch with no functional change. Reviewed-by: Pankaj Gupta > --- > mm/compaction.c | 3 ++- > mm/internal.h | 14 +++++++++++--- > mm/page_alloc.c | 40 +++++++++++++++++++++++----------------- > 3 files changed, 36 insertions(+), 21 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 32623894a6327..25371a75471dd 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -2358,7 +2358,8 @@ static enum compact_result __compact_finished(struct compact_control *cc) > * Job done if allocation would steal freepages from > * other migratetype buddy lists. > */ > - if (find_suitable_fallback(area, order, migratetype, true) >= 0) > + if (find_suitable_fallback(area, order, migratetype, true, NULL) > + == FALLBACK_FOUND) > /* > * Movable pages are OK in any pageblock. If we are > * stealing for a non-movable allocation, make sure > diff --git a/mm/internal.h b/mm/internal.h > index f4c59534670e4..e3782721a588b 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -1059,9 +1059,17 @@ static inline void init_cma_pageblock(struct page *page) > } > #endif > > - > -int find_suitable_fallback(struct free_area *area, unsigned int order, > - int migratetype, bool claimable); > +enum fallback_result { > + /* Found suitable migratetype, *mt_out is valid. */ > + FALLBACK_FOUND, > + /* No fallback found in requested order. */ > + FALLBACK_EMPTY, > + /* Passed @claimable, but claiming whole block is a bad idea. */ > + FALLBACK_NOCLAIM, > +}; > +enum fallback_result > +find_suitable_fallback(struct free_area *area, unsigned int order, > + int migratetype, bool claimable, unsigned int *mt_out); > > static inline bool free_area_empty(struct free_area *area, int migratetype) > { > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 0a1dc7866068f..ac077d98019f3 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2248,25 +2248,29 @@ static bool should_try_claim_block(unsigned int order, int start_mt) > * we would do this whole-block claiming. This would help to reduce > * fragmentation due to mixed migratetype pages in one pageblock. > */ > -int find_suitable_fallback(struct free_area *area, unsigned int order, > - int migratetype, bool claimable) > +enum fallback_result > +find_suitable_fallback(struct free_area *area, unsigned int order, > + int migratetype, bool claimable, unsigned int *mt_out) > { > int i; > > if (claimable && !should_try_claim_block(order, migratetype)) > - return -2; > + return FALLBACK_NOCLAIM; > > if (area->nr_free == 0) > - return -1; > + return FALLBACK_EMPTY; > > for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) { > int fallback_mt = fallbacks[migratetype][i]; > > - if (!free_area_empty(area, fallback_mt)) > - return fallback_mt; > + if (!free_area_empty(area, fallback_mt)) { > + if (mt_out) > + *mt_out = fallback_mt; > + return FALLBACK_FOUND; > + } > } > > - return -1; > + return FALLBACK_EMPTY; > } > > /* > @@ -2376,16 +2380,16 @@ __rmqueue_claim(struct zone *zone, int order, int start_migratetype, > */ > for (current_order = MAX_PAGE_ORDER; current_order >= min_order; > --current_order) { > - area = &(zone->free_area[current_order]); > - fallback_mt = find_suitable_fallback(area, current_order, > - start_migratetype, true); > + enum fallback_result result; > > - /* No block in that order */ > - if (fallback_mt == -1) > + area = &(zone->free_area[current_order]); > + result = find_suitable_fallback(area, current_order, > + start_migratetype, true, &fallback_mt); > + > + if (result == FALLBACK_EMPTY) > continue; > > - /* Advanced into orders too low to claim, abort */ > - if (fallback_mt == -2) > + if (result == FALLBACK_NOCLAIM) > break; > > page = get_page_from_free_area(area, fallback_mt); > @@ -2415,10 +2419,12 @@ __rmqueue_steal(struct zone *zone, int order, int start_migratetype) > int fallback_mt; > > for (current_order = order; current_order < NR_PAGE_ORDERS; current_order++) { > + enum fallback_result result; > + > area = &(zone->free_area[current_order]); > - fallback_mt = find_suitable_fallback(area, current_order, > - start_migratetype, false); > - if (fallback_mt == -1) > + result = find_suitable_fallback(area, current_order, start_migratetype, > + false, &fallback_mt); > + if (result == FALLBACK_EMPTY) > continue; > > page = get_page_from_free_area(area, fallback_mt); >