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#author("2025-09-11T11:07:49+09:00","default:guest","guest") #author("2025-09-11T11:20:02+09:00","default:guest","guest") *参照元 [#cb8cc65f] #backlinks *説明 [#s64e2f94] -パス: [[linux-5.15/mm/compaction.c]] -FIXME: これは何？ --説明 -指定したゾーン、オーダー、割当フラグにおいて、コンパクションを行うかどうかを取得する。 **引数 [#c9a3a281] - -- -struct zone *zone --メモリゾーン。 --[[linux-5.15/zone]] -int order --オーダー -unsigned int alloc_flags --割当フラグ -int highest_zoneidx --この値以下のゾーンから割り当てる **返り値 [#wc1d1b93] - -- -enum compact_result --COMPACT_SKIPPED - コンパクションするための空きページが足りない（のでコンパクションしない） --COMPACT_SUCCESS - コンパクションしなくても割当が成功する（のでコンパクションしない） --COMPACT_CONTINUE - コンパクションすべき **参考 [#c767d3fd] *実装 [#fd42e6cf] /* * compaction_suitable: Is this suitable to run compaction on this zone now? * Returns * COMPACT_SKIPPED - If there are too few free pages for compaction * COMPACT_SUCCESS - If the allocation would succeed without compaction * COMPACT_CONTINUE - If compaction should run now */ enum compact_result compaction_suitable(struct zone *zone, int order, unsigned int alloc_flags, int highest_zoneidx) { enum compact_result ret; int fragindex; ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx, zone_page_state(zone, NR_FREE_PAGES)); - --[[linux-5.15/__compaction_suitable()]] --[[linux-5.15/zone_page_state()]] /* * fragmentation index determines if allocation failures are due to * low memory or external fragmentation * * index of -1000 would imply allocations might succeed depending on * watermarks, but we already failed the high-order watermark check * index towards 0 implies failure is due to lack of memory * index towards 1000 implies failure is due to fragmentation * * Only compact if a failure would be due to fragmentation. Also * ignore fragindex for non-costly orders where the alternative to * a successful reclaim/compaction is OOM. Fragindex and the * vm.extfrag_threshold sysctl is meant as a heuristic to prevent * excessive compaction for costly orders, but it should not be at the * expense of system stability. */ if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) { fragindex = fragmentation_index(zone, order); if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold) ret = COMPACT_NOT_SUITABLE_ZONE; } - --[[linux-5.15/fragmentation_index()]] trace_mm_compaction_suitable(zone, order, ret); if (ret == COMPACT_NOT_SUITABLE_ZONE) ret = COMPACT_SKIPPED; return ret; } - --[[linux-5.15/trace_mm_compaction_suitable()]] *コメント [#cb4b6f63]
