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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'll
search higher bins if necessary while allocating next time, and
also eventually re-bin, so no memory can become unreachable that way.

However, when freeing memory, the largest contiguous range of free pages
might go up, so we should re-bin eagerly to make sure we don't leave the
segment 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 be
called 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
This commit is contained in:
Thomas Munro 2023-07-04 15:16:34 +12:00
parent 13f127800f
commit 1605623ec6
1 changed files with 43 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

65
src/backend/utils/mmgr/dsa.c
View File

@ -406,6 +406,7 @@ static dsa_area *attach_internal(void *place, dsm_segment *segment,
dsa_handle handle);
static void check_for_freed_segments(dsa_area *area);
static void check_for_freed_segments_locked(dsa_area *area);
static void rebin_segment(dsa_area *area, dsa_segment_map *segment_map);
/*
* 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)
FreePageManagerPut(segment_map->fpm,
DSA_EXTRACT_OFFSET(span->start) / FPM_PAGE_SIZE,
span->npages);
/* Move segment to appropriate bin if necessary. */
rebin_segment(area, segment_map);
LWLockRelease(DSA_AREA_LOCK(area));
/* Unlink span. */
LWLockAcquire(DSA_SCLASS_LOCK(area, DSA_SCLASS_SPAN_LARGE),
LW_EXCLUSIVE);
@ -1848,6 +1853,11 @@ destroy_superblock(dsa_area *area, dsa_pointer span_pointer)
segment_map->mapped_address = NULL;
}
}
/* Move segment to appropriate bin if necessary. */
if (segment_map->header != NULL)
rebin_segment(area, segment_map);
LWLockRelease(DSA_AREA_LOCK(area));
/*
@ -2011,28 +2021,7 @@ get_best_segment(dsa_area *area, size_t npages)
/* Re-bin it if it's no longer in the appropriate bin. */
if (contiguous_pages < threshold)
{
size_t new_bin;
new_bin = contiguous_pages_to_segment_bin(contiguous_pages);
/* Remove it from its current bin. */
unlink_segment(area, segment_map);
/* Push it onto the front of its new bin. */
segment_map->header->prev = DSA_SEGMENT_INDEX_NONE;
segment_map->header->next =
area->control->segment_bins[new_bin];
segment_map->header->bin = new_bin;
area->control->segment_bins[new_bin] = segment_index;
if (segment_map->header->next != DSA_SEGMENT_INDEX_NONE)
{
dsa_segment_map *next;
next = get_segment_by_index(area,
segment_map->header->next);
Assert(next->header->bin == new_bin);
next->header->prev = segment_index;
}
rebin_segment(area, segment_map);
/*
* But fall through to see if it's enough to satisfy this
@ -2287,3 +2276,35 @@ check_for_freed_segments_locked(dsa_area *area)
area->freed_segment_counter = freed_segment_counter;
}
}
/*
* Re-bin segment if it's no longer in the appropriate bin.
*/
static void
rebin_segment(dsa_area *area, dsa_segment_map *segment_map)
{
size_t new_bin;
dsa_segment_index segment_index;
new_bin = contiguous_pages_to_segment_bin(fpm_largest(segment_map->fpm));
if (segment_map->header->bin == new_bin)
return;
/* Remove it from its current bin. */
unlink_segment(area, segment_map);
/* Push it onto the front of its new bin. */
segment_index = get_segment_index(area, segment_map);
segment_map->header->prev = DSA_SEGMENT_INDEX_NONE;
segment_map->header->next = area->control->segment_bins[new_bin];
segment_map->header->bin = new_bin;
area->control->segment_bins[new_bin] = segment_index;
if (segment_map->header->next != DSA_SEGMENT_INDEX_NONE)
{
dsa_segment_map *next;
next = get_segment_by_index(area, segment_map->header->next);
Assert(next->header->bin == new_bin);
next->header->prev = segment_index;
}
}