Allow specifying initial and maximum segment sizes for DSA.

Previously, the DSA segment size always started with 1MB and grew up
to DSA_MAX_SEGMENT_SIZE. It was inconvenient in certain scenarios,
such as when the caller desired a soft constraint on the total DSA
segment size, limiting it to less than 1MB.

This commit introduces the capability to specify the initial and
maximum DSA segment sizes when creating a DSA area, providing more
flexibility and control over memory usage.

Reviewed-by: John Naylor, Tomas Vondra
Discussion: https://postgr.es/m/CAD21AoAYGGC1ePjVX0H%2Bpp9rH%3D9vuPK19nNOiu12NprdV5TVJA%40mail.gmail.com

diff --git a/src/backend/utils/mmgr/dsa.c b/src/backend/utils/mmgr/dsa.c
index c3af0719404948e74879c662184735205676bf64..2d4639a63622f728551d4750c75ce36a58009141 100644 (file)
--- a/src/backend/utils/mmgr/dsa.c
+++ b/src/backend/utils/mmgr/dsa.c
@@ -59,14 +59,6 @@
 #include "utils/memutils.h"
 #include "utils/resowner.h"
 
-/*
- * The size of the initial DSM segment that backs a dsa_area created by
- * dsa_create.  After creating some number of segments of this size we'll
- * double this size, and so on.  Larger segments may be created if necessary
- * to satisfy large requests.
- */
-#define DSA_INITIAL_SEGMENT_SIZE ((size_t) (1 * 1024 * 1024))
-
 /*
  * How many segments to create before we double the segment size.  If this is
  * low, then there is likely to be a lot of wasted space in the largest
@@ -76,17 +68,6 @@
  */
 #define DSA_NUM_SEGMENTS_AT_EACH_SIZE 2
 
-/*
- * The number of bits used to represent the offset part of a dsa_pointer.
- * This controls the maximum size of a segment, the maximum possible
- * allocation size and also the maximum number of segments per area.
- */
-#if SIZEOF_DSA_POINTER == 4
-#define DSA_OFFSET_WIDTH 27        /* 32 segments of size up to 128MB */
-#else
-#define DSA_OFFSET_WIDTH 40        /* 1024 segments of size up to 1TB */
-#endif
-
 /*
  * The maximum number of DSM segments that an area can own, determined by
  * the number of bits remaining (but capped at 1024).
@@ -97,9 +78,6 @@
 /* The bitmask for extracting the offset from a dsa_pointer. */
 #define DSA_OFFSET_BITMASK (((dsa_pointer) 1 << DSA_OFFSET_WIDTH) - 1)
 
-/* The maximum size of a DSM segment. */
-#define DSA_MAX_SEGMENT_SIZE ((size_t) 1 << DSA_OFFSET_WIDTH)
-
 /* Number of pages (see FPM_PAGE_SIZE) per regular superblock. */
 #define DSA_PAGES_PER_SUPERBLOCK       16
 
@@ -318,6 +296,10 @@ typedef struct
    dsa_segment_index segment_bins[DSA_NUM_SEGMENT_BINS];
    /* The object pools for each size class. */
    dsa_area_pool pools[DSA_NUM_SIZE_CLASSES];
+   /* initial allocation segment size */
+   size_t      init_segment_size;
+   /* maximum allocation segment size */
+   size_t      max_segment_size;
    /* The total size of all active segments. */
    size_t      total_segment_size;
    /* The maximum total size of backing storage we are allowed. */
@@ -417,7 +399,9 @@ static dsa_segment_map *make_new_segment(dsa_area *area, size_t requested_pages)
 static dsa_area *create_internal(void *place, size_t size,
                                 int tranche_id,
                                 dsm_handle control_handle,
-                                dsm_segment *control_segment);
+                                dsm_segment *control_segment,
+                                size_t init_segment_size,
+                                size_t max_segment_size);
 static dsa_area *attach_internal(void *place, dsm_segment *segment,
                                 dsa_handle handle);
 static void check_for_freed_segments(dsa_area *area);
@@ -434,7 +418,7 @@ static void rebin_segment(dsa_area *area, dsa_segment_map *segment_map);
  * we require the caller to provide one.
  */
 dsa_area *
-dsa_create(int tranche_id)
+dsa_create_ext(int tranche_id, size_t init_segment_size, size_t max_segment_size)
 {
    dsm_segment *segment;
    dsa_area   *area;
@@ -443,7 +427,7 @@ dsa_create(int tranche_id)
     * Create the DSM segment that will hold the shared control object and the
     * first segment of usable space.
     */
-   segment = dsm_create(DSA_INITIAL_SEGMENT_SIZE, 0);
+   segment = dsm_create(init_segment_size, 0);
 
    /*
     * All segments backing this area are pinned, so that DSA can explicitly
@@ -455,9 +439,10 @@ dsa_create(int tranche_id)
 
    /* Create a new DSA area with the control object in this segment. */
    area = create_internal(dsm_segment_address(segment),
-                          DSA_INITIAL_SEGMENT_SIZE,
+                          init_segment_size,
                           tranche_id,
-                          dsm_segment_handle(segment), segment);
+                          dsm_segment_handle(segment), segment,
+                          init_segment_size, max_segment_size);
 
    /* Clean up when the control segment detaches. */
    on_dsm_detach(segment, &dsa_on_dsm_detach_release_in_place,
@@ -483,13 +468,15 @@ dsa_create(int tranche_id)
  * See dsa_create() for a note about the tranche arguments.
  */
 dsa_area *
-dsa_create_in_place(void *place, size_t size,
-                   int tranche_id, dsm_segment *segment)
+dsa_create_in_place_ext(void *place, size_t size,
+                       int tranche_id, dsm_segment *segment,
+                       size_t init_segment_size, size_t max_segment_size)
 {
    dsa_area   *area;
 
    area = create_internal(place, size, tranche_id,
-                          DSM_HANDLE_INVALID, NULL);
+                          DSM_HANDLE_INVALID, NULL,
+                          init_segment_size, max_segment_size);
 
    /*
     * Clean up when the control segment detaches, if a containing DSM segment
@@ -1231,7 +1218,8 @@ static dsa_area *
 create_internal(void *place, size_t size,
                int tranche_id,
                dsm_handle control_handle,
-               dsm_segment *control_segment)
+               dsm_segment *control_segment,
+               size_t init_segment_size, size_t max_segment_size)
 {
    dsa_area_control *control;
    dsa_area   *area;
@@ -1241,6 +1229,11 @@ create_internal(void *place, size_t size,
    size_t      metadata_bytes;
    int         i;
 
+   /* Check the initial and maximum block sizes */
+   Assert(init_segment_size >= DSA_MIN_SEGMENT_SIZE);
+   Assert(max_segment_size >= init_segment_size);
+   Assert(max_segment_size <= DSA_MAX_SEGMENT_SIZE);
+
    /* Sanity check on the space we have to work in. */
    if (size < dsa_minimum_size())
        elog(ERROR, "dsa_area space must be at least %zu, but %zu provided",
@@ -1270,8 +1263,10 @@ create_internal(void *place, size_t size,
    control->segment_header.prev = DSA_SEGMENT_INDEX_NONE;
    control->segment_header.usable_pages = usable_pages;
    control->segment_header.freed = false;
-   control->segment_header.size = DSA_INITIAL_SEGMENT_SIZE;
+   control->segment_header.size = size;
    control->handle = control_handle;
+   control->init_segment_size = init_segment_size;
+   control->max_segment_size = max_segment_size;
    control->max_total_segment_size = (size_t) -1;
    control->total_segment_size = size;
    control->segment_handles[0] = control_handle;
@@ -2127,9 +2122,9 @@ make_new_segment(dsa_area *area, size_t requested_pages)
     * move to huge pages in the future.  Then we work back to the number of
     * pages we can fit.
     */
-   total_size = DSA_INITIAL_SEGMENT_SIZE *
+   total_size = area->control->init_segment_size *
        ((size_t) 1 << (new_index / DSA_NUM_SEGMENTS_AT_EACH_SIZE));
-   total_size = Min(total_size, DSA_MAX_SEGMENT_SIZE);
+   total_size = Min(total_size, area->control->max_segment_size);
    total_size = Min(total_size,
                     area->control->max_total_segment_size -
                     area->control->total_segment_size);

diff --git a/src/include/utils/dsa.h b/src/include/utils/dsa.h
index fe9cbebbec1a43ed575afcf740d8bbff27f6f5ac..8dff964bf3334c908e566fe455f0015ae7d0e8b0 100644 (file)
--- a/src/include/utils/dsa.h
+++ b/src/include/utils/dsa.h
@@ -77,6 +77,31 @@ typedef pg_atomic_uint64 dsa_pointer_atomic;
 /* A sentinel value for dsa_pointer used to indicate failure to allocate. */
 #define InvalidDsaPointer ((dsa_pointer) 0)
 
+/*
+ * The number of bits used to represent the offset part of a dsa_pointer.
+ * This controls the maximum size of a segment, the maximum possible
+ * allocation size and also the maximum number of segments per area.
+ */
+#if SIZEOF_DSA_POINTER == 4
+#define DSA_OFFSET_WIDTH 27        /* 32 segments of size up to 128MB */
+#else
+#define DSA_OFFSET_WIDTH 40        /* 1024 segments of size up to 1TB */
+#endif
+
+/*
+ * The default size of the initial DSM segment that backs a dsa_area created
+ * by dsa_create.  After creating some number of segments of the initial size
+ * we'll double this size, and so on.  Larger segments may be created if
+ * necessary to satisfy large requests.
+ */
+#define DSA_DEFAULT_INIT_SEGMENT_SIZE ((size_t) (1 * 1024 * 1024))
+
+/* The minimum size of a DSM segment. */
+#define DSA_MIN_SEGMENT_SIZE   ((size_t) (256 * 1024L))
+
+/* The maximum size of a DSM segment. */
+#define DSA_MAX_SEGMENT_SIZE ((size_t) 1 << DSA_OFFSET_WIDTH)
+
 /* Check if a dsa_pointer value is valid. */
 #define DsaPointerIsValid(x) ((x) != InvalidDsaPointer)
 
@@ -88,6 +113,17 @@ typedef pg_atomic_uint64 dsa_pointer_atomic;
 #define dsa_allocate0(area, size) \
    dsa_allocate_extended(area, size, DSA_ALLOC_ZERO)
 
+/* Create dsa_area with default segment sizes */
+#define dsa_create(tranch_id) \
+   dsa_create_ext(tranch_id, DSA_DEFAULT_INIT_SEGMENT_SIZE, \
+                  DSA_MAX_SEGMENT_SIZE)
+
+/* Create dsa_area with default segment sizes in an existing share memory space */
+#define dsa_create_in_place(place, size, tranch_id, segment) \
+   dsa_create_in_place_ext(place, size, tranch_id, segment, \
+                           DSA_DEFAULT_INIT_SEGMENT_SIZE, \
+                           DSA_MAX_SEGMENT_SIZE)
+
 /*
  * The type used for dsa_area handles.  dsa_handle values can be shared with
  * other processes, so that they can attach to them.  This provides a way to
@@ -102,10 +138,12 @@ typedef dsm_handle dsa_handle;
 /* Sentinel value to use for invalid dsa_handles. */
 #define DSA_HANDLE_INVALID ((dsa_handle) DSM_HANDLE_INVALID)
 
-
-extern dsa_area *dsa_create(int tranche_id);
-extern dsa_area *dsa_create_in_place(void *place, size_t size,
-                                    int tranche_id, dsm_segment *segment);
+extern dsa_area *dsa_create_ext(int tranche_id, size_t init_segment_size,
+                               size_t max_segment_size);
+extern dsa_area *dsa_create_in_place_ext(void *place, size_t size,
+                                        int tranche_id, dsm_segment *segment,
+                                        size_t init_segment_size,
+                                        size_t max_segment_size);
 extern dsa_area *dsa_attach(dsa_handle handle);
 extern dsa_area *dsa_attach_in_place(void *place, dsm_segment *segment);
 extern void dsa_release_in_place(void *place);