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List-Subscribe: List-Unsubscribe: On Thu, Apr 23, 2026 at 04:04:32PM +1000, Balbir Singh wrote: > On 4/23/26 15:56, Matthew Brost wrote: > > Introduce zone_appears_fragmented() as a lightweight helper to allow > > subsystems to make coarse decisions about reclaim behavior in the > > presence of likely fragmentation. > > > > The helper implements a simple heuristic: if the number of free pages > > in a zone exceeds twice the high watermark, the zone is considered to > > have ample free memory and allocation failures are more likely due to > > fragmentation than overall memory pressure. > > > > This is intentionally imprecise and is not meant to replace the core > > MM compaction or fragmentation accounting logic. Instead, it provides > > a cheap signal for callers (e.g., shrinkers) that wish to avoid > > overly aggressive reclaim when sufficient free memory exists but > > high-order allocations may still fail. > > > > No functional changes; this is a preparatory helper for future users. > > > > Cc: Thomas Hellström > > Cc: Andrew Morton > > Cc: David Hildenbrand > > Cc: Lorenzo Stoakes > > Cc: "Liam R. Howlett" > > Cc: Vlastimil Babka > > Cc: Mike Rapoport > > Cc: Suren Baghdasaryan > > Cc: Michal Hocko > > Cc: linux-mm@kvack.org > > Cc: linux-kernel@vger.kernel.org > > Signed-off-by: Matthew Brost > > --- > > include/linux/vmstat.h | 13 +++++++++++++ > > 1 file changed, 13 insertions(+) > > > > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h > > index 3c9c266cf782..568d9f4f1a1f 100644 > > --- a/include/linux/vmstat.h > > +++ b/include/linux/vmstat.h > > @@ -483,6 +483,19 @@ static inline const char *zone_stat_name(enum zone_stat_item item) > > return vmstat_text[item]; > > } > > > > +static inline bool zone_appears_fragmented(struct zone *zone) > > +{ > > + /* > > + * Simple heuristic: if the number of free pages is more than twice the > > + * high watermark, this strongly suggests that the zone is heavily > > + * fragmented when called from a shrinker. > > + */ > > + if (zone_page_state(zone, NR_FREE_PAGES) > high_wmark_pages(zone) * 2) > > + return true; > > + > > + return false; > > +} > > + > > #ifdef CONFIG_NUMA > > static inline const char *numa_stat_name(enum numa_stat_item item) > > { > > > Without any usage/users, this is hard to review. I don't understand the heuristic > or it's logic as applied to fragmentation either. > Sorry—it’s always confusing who to CC on cross-subsystem series. Last time this occurred, we agreed to CC everyone listed in the cover letter, which I did. Anyway, let me provide the Patchwork links... Cover letter: https://patchwork.freedesktop.org/series/165329/ TTM patch which uses this: https://patchwork.freedesktop.org/patch/720036/?series=165329&rev=1 Xe side which uses the TTM helper: https://patchwork.freedesktop.org/patch/720031/?series=165329&rev=1 Matt > Balbir