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Commitb7ec667

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Re-bin segment when memory pages are freed.
It's OK to be lazy about re-binning memory segments when allocating,because that can only leave segments in a bin that's too high. We'llsearch higher bins if necessary while allocating next time, andalso eventually re-bin, so no memory can become unreachable that way.However, when freeing memory, the largest contiguous range of free pagesmight go up, so we should re-bin eagerly to make sure we don't leave thesegment in a bin that is too low for get_best_segment() to find.The re-binning code is moved into a function of its own, so it can becalled whenever free pages are returned to the segment's free page map.Back-patch to all supported releases.Author: Dongming Liu <ldming101@gmail.com>Reviewed-by: Robert Haas <robertmhaas@gmail.com> (earlier version)Reviewed-by: Thomas Munro <thomas.munro@gmail.com>Discussion:https://postgr.es/m/CAL1p7e8LzB2LSeAXo2pXCW4%2BRya9s0sJ3G_ReKOU%3DAjSUWjHWQ%40mail.gmail.com
1 parentfb663f3 commitb7ec667

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1 file changed

+43
-22
lines changed
  • src/backend/utils/mmgr

1 file changed

+43
-22
lines changed

‎src/backend/utils/mmgr/dsa.c‎

Lines changed: 43 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -406,6 +406,7 @@ static dsa_area *attach_internal(void *place, dsm_segment *segment,
406406
dsa_handlehandle);
407407
staticvoidcheck_for_freed_segments(dsa_area*area);
408408
staticvoidcheck_for_freed_segments_locked(dsa_area*area);
409+
staticvoidrebin_segment(dsa_area*area,dsa_segment_map*segment_map);
409410

410411
/*
411412
* Create a new shared area in a new DSM segment. Further DSM segments will
@@ -857,7 +858,11 @@ dsa_free(dsa_area *area, dsa_pointer dp)
857858
FreePageManagerPut(segment_map->fpm,
858859
DSA_EXTRACT_OFFSET(span->start) /FPM_PAGE_SIZE,
859860
span->npages);
861+
862+
/* Move segment to appropriate bin if necessary. */
863+
rebin_segment(area,segment_map);
860864
LWLockRelease(DSA_AREA_LOCK(area));
865+
861866
/* Unlink span. */
862867
LWLockAcquire(DSA_SCLASS_LOCK(area,DSA_SCLASS_SPAN_LARGE),
863868
LW_EXCLUSIVE);
@@ -1846,6 +1851,11 @@ destroy_superblock(dsa_area *area, dsa_pointer span_pointer)
18461851
segment_map->mapped_address=NULL;
18471852
}
18481853
}
1854+
1855+
/* Move segment to appropriate bin if necessary. */
1856+
if (segment_map->header!=NULL)
1857+
rebin_segment(area,segment_map);
1858+
18491859
LWLockRelease(DSA_AREA_LOCK(area));
18501860

18511861
/*
@@ -2009,28 +2019,7 @@ get_best_segment(dsa_area *area, size_t npages)
20092019
/* Re-bin it if it's no longer in the appropriate bin. */
20102020
if (contiguous_pages<threshold)
20112021
{
2012-
size_tnew_bin;
2013-
2014-
new_bin=contiguous_pages_to_segment_bin(contiguous_pages);
2015-
2016-
/* Remove it from its current bin. */
2017-
unlink_segment(area,segment_map);
2018-
2019-
/* Push it onto the front of its new bin. */
2020-
segment_map->header->prev=DSA_SEGMENT_INDEX_NONE;
2021-
segment_map->header->next=
2022-
area->control->segment_bins[new_bin];
2023-
segment_map->header->bin=new_bin;
2024-
area->control->segment_bins[new_bin]=segment_index;
2025-
if (segment_map->header->next!=DSA_SEGMENT_INDEX_NONE)
2026-
{
2027-
dsa_segment_map*next;
2028-
2029-
next=get_segment_by_index(area,
2030-
segment_map->header->next);
2031-
Assert(next->header->bin==new_bin);
2032-
next->header->prev=segment_index;
2033-
}
2022+
rebin_segment(area,segment_map);
20342023

20352024
/*
20362025
* But fall through to see if it's enough to satisfy this
@@ -2285,3 +2274,35 @@ check_for_freed_segments_locked(dsa_area *area)
22852274
area->freed_segment_counter=freed_segment_counter;
22862275
}
22872276
}
2277+
2278+
/*
2279+
* Re-bin segment if it's no longer in the appropriate bin.
2280+
*/
2281+
staticvoid
2282+
rebin_segment(dsa_area*area,dsa_segment_map*segment_map)
2283+
{
2284+
size_tnew_bin;
2285+
dsa_segment_indexsegment_index;
2286+
2287+
new_bin=contiguous_pages_to_segment_bin(fpm_largest(segment_map->fpm));
2288+
if (segment_map->header->bin==new_bin)
2289+
return;
2290+
2291+
/* Remove it from its current bin. */
2292+
unlink_segment(area,segment_map);
2293+
2294+
/* Push it onto the front of its new bin. */
2295+
segment_index=get_segment_index(area,segment_map);
2296+
segment_map->header->prev=DSA_SEGMENT_INDEX_NONE;
2297+
segment_map->header->next=area->control->segment_bins[new_bin];
2298+
segment_map->header->bin=new_bin;
2299+
area->control->segment_bins[new_bin]=segment_index;
2300+
if (segment_map->header->next!=DSA_SEGMENT_INDEX_NONE)
2301+
{
2302+
dsa_segment_map*next;
2303+
2304+
next=get_segment_by_index(area,segment_map->header->next);
2305+
Assert(next->header->bin==new_bin);
2306+
next->header->prev=segment_index;
2307+
}
2308+
}

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