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Message-ID: <5f3ad5f3-780d-1ff7-5f97-0dc8b5611581@suse.cz>
Date: Mon, 29 May 2023 19:11:35 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Johannes Weiner <hannes@...xchg.org>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>,
Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 3/5] mm: compaction: refactor __compaction_suitable()
On 5/19/23 14:39, Johannes Weiner wrote:
> __compaction_suitable() is supposed to check for available migration
> targets. However, it also checks whether the operation was requested
> via /proc/sys/vm/compact_memory, and whether the original allocation
> request can already succeed. These don't apply to all callsites.
>
> Move the checks out to the callers, so that later patches can deal
> with them one by one. No functional change intended.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Note comment on compaction_suitable() still mentions COMPACT_SUCCESS, that
is no longer possible, so delete that line?
Also on closer look, both compaction_suitable() and __compaction_suitable()
could now simply return bool. The callers use it that way anyway. There
would just be some extra fiddling internally aroud the tracepoint.
> ---
> include/linux/compaction.h | 4 +-
> mm/compaction.c | 78 ++++++++++++++++++++++++--------------
> mm/vmscan.c | 35 ++++++++++-------
> 3 files changed, 73 insertions(+), 44 deletions(-)
>
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index 1f0328a2ba48..9f7cf3e1bf89 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -90,7 +90,7 @@ extern enum compact_result try_to_compact_pages(gfp_t gfp_mask,
> struct page **page);
> extern void reset_isolation_suitable(pg_data_t *pgdat);
> extern enum compact_result compaction_suitable(struct zone *zone, int order,
> - unsigned int alloc_flags, int highest_zoneidx);
> + int highest_zoneidx);
>
> extern void compaction_defer_reset(struct zone *zone, int order,
> bool alloc_success);
> @@ -108,7 +108,7 @@ static inline void reset_isolation_suitable(pg_data_t *pgdat)
> }
>
> static inline enum compact_result compaction_suitable(struct zone *zone, int order,
> - int alloc_flags, int highest_zoneidx)
> + int highest_zoneidx)
> {
> return COMPACT_SKIPPED;
> }
> diff --git a/mm/compaction.c b/mm/compaction.c
> index c9a4b6dffcf2..8f61cfa87c49 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -2206,24 +2206,10 @@ static enum compact_result compact_finished(struct compact_control *cc)
> }
>
> static enum compact_result __compaction_suitable(struct zone *zone, int order,
> - unsigned int alloc_flags,
> int highest_zoneidx,
> unsigned long wmark_target)
> {
> unsigned long watermark;
> -
> - if (is_via_compact_memory(order))
> - return COMPACT_CONTINUE;
> -
> - watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
> - /*
> - * If watermarks for high-order allocation are already met, there
> - * should be no need for compaction at all.
> - */
> - if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
> - alloc_flags))
> - return COMPACT_SUCCESS;
> -
> /*
> * Watermarks for order-0 must be met for compaction to be able to
> * isolate free pages for migration targets. This means that the
> @@ -2256,13 +2242,12 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
> * 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,
> + ret = __compaction_suitable(zone, order, highest_zoneidx,
> zone_page_state(zone, NR_FREE_PAGES));
> /*
> * fragmentation index determines if allocation failures are due to
> @@ -2306,7 +2291,16 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
> for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
> ac->highest_zoneidx, ac->nodemask) {
> unsigned long available;
> - enum compact_result compact_result;
> + unsigned long watermark;
> +
> + if (is_via_compact_memory(order))
> + return true;
> +
> + /* Allocation can already succeed, nothing to do */
> + watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
> + if (zone_watermark_ok(zone, order, watermark,
> + ac->highest_zoneidx, alloc_flags))
> + continue;
>
> /*
> * Do not consider all the reclaimable memory because we do not
> @@ -2316,9 +2310,8 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
> */
> available = zone_reclaimable_pages(zone) / order;
> available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
> - compact_result = __compaction_suitable(zone, order, alloc_flags,
> - ac->highest_zoneidx, available);
> - if (compact_result == COMPACT_CONTINUE)
> + if (__compaction_suitable(zone, order, ac->highest_zoneidx,
> + available) == COMPACT_CONTINUE)
> return true;
> }
>
> @@ -2348,11 +2341,23 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
> INIT_LIST_HEAD(&cc->migratepages);
>
> cc->migratetype = gfp_migratetype(cc->gfp_mask);
> - ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
> - cc->highest_zoneidx);
> - /* Compaction is likely to fail */
> - if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
> - return ret;
> +
> + if (!is_via_compact_memory(cc->order)) {
> + unsigned long watermark;
> +
> + /* Allocation can already succeed, nothing to do */
> + watermark = wmark_pages(cc->zone,
> + cc->alloc_flags & ALLOC_WMARK_MASK);
> + if (zone_watermark_ok(cc->zone, cc->order, watermark,
> + cc->highest_zoneidx, cc->alloc_flags))
> + return COMPACT_SUCCESS;
> +
> + ret = compaction_suitable(cc->zone, cc->order,
> + cc->highest_zoneidx);
> + /* Compaction is likely to fail */
> + if (ret == COMPACT_SKIPPED)
> + return ret;
> + }
>
> /*
> * Clear pageblock skip if there were failures recently and compaction
> @@ -2845,7 +2850,16 @@ static bool kcompactd_node_suitable(pg_data_t *pgdat)
> if (!populated_zone(zone))
> continue;
>
> - if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
> + if (is_via_compact_memory(pgdat->kcompactd_max_order))
> + return true;
> +
> + /* Allocation can already succeed, check other zones */
> + if (zone_watermark_ok(zone, pgdat->kcompactd_max_order,
> + min_wmark_pages(zone),
> + highest_zoneidx, 0))
> + continue;
> +
> + if (compaction_suitable(zone, pgdat->kcompactd_max_order,
> highest_zoneidx) == COMPACT_CONTINUE)
> return true;
> }
> @@ -2883,10 +2897,18 @@ static void kcompactd_do_work(pg_data_t *pgdat)
> if (compaction_deferred(zone, cc.order))
> continue;
>
> - if (compaction_suitable(zone, cc.order, 0, zoneid) !=
> - COMPACT_CONTINUE)
> + if (is_via_compact_memory(cc.order))
> + goto compact;
> +
> + /* Allocation can already succeed, nothing to do */
> + if (zone_watermark_ok(zone, cc.order,
> + min_wmark_pages(zone), zoneid, 0))
> continue;
>
> + if (compaction_suitable(zone, cc.order,
> + zoneid) != COMPACT_CONTINUE)
> + continue;
> +compact:
> if (kthread_should_stop())
> return;
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index d257916f39e5..c9c0f3e081f5 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -6397,14 +6397,17 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
> if (!managed_zone(zone))
> continue;
>
> - switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
> - case COMPACT_SUCCESS:
> - case COMPACT_CONTINUE:
> + if (sc->order == -1) /* is_via_compact_memory() */
> + return false;
> +
> + /* Allocation can already succeed, nothing to do */
> + if (zone_watermark_ok(zone, sc->order, min_wmark_pages(zone),
> + sc->reclaim_idx, 0))
> + return false;
> +
> + if (compaction_suitable(zone, sc->order,
> + sc->reclaim_idx) == COMPACT_CONTINUE)
> return false;
> - default:
> - /* check next zone */
> - ;
> - }
> }
>
> /*
> @@ -6592,16 +6595,20 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
> {
> unsigned long watermark;
> - enum compact_result suitable;
>
> - suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
> - if (suitable == COMPACT_SUCCESS)
> - /* Allocation should succeed already. Don't reclaim. */
> + if (sc->order == -1) /* is_via_compact_memory() */
> + goto suitable;
> +
> + /* Allocation can already succeed, nothing to do */
> + if (zone_watermark_ok(zone, sc->order, min_wmark_pages(zone),
> + sc->reclaim_idx, 0))
> return true;
> - if (suitable == COMPACT_SKIPPED)
> - /* Compaction cannot yet proceed. Do reclaim. */
> - return false;
>
> + /* Compaction cannot yet proceed. Do reclaim. */
> + if (compaction_suitable(zone, sc->order,
> + sc->reclaim_idx) == COMPACT_SKIPPED)
> + return false;
> +suitable:
> /*
> * Compaction is already possible, but it takes time to run and there
> * are potentially other callers using the pages just freed. So proceed
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