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Allocate history buffer segments with mmap

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glibc can raise its dynamic mmap threshold above these MB-scale allocations, routing later scrollback segments through brk. Closing windows then leaves the freed segments stranded in allocator bins and grows the long-lived kitty process.

Back the existing batched segment layout with anonymous mappings instead. This preserves zero-initialization and pointer layout while ensuring the memory is returned to the OS when a history buffer is cleared or destroyed.

Co-Authored-By: Claude <noreply@anthropic.com>
This commit is contained in:
Sinity
2026-07-11 21:46:30 +02:00
parent 2607d22ac3
commit d96752e0f1
2 changed files with 10 additions and 3 deletions
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12
kitty/history.c
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@@ -10,6 +10,7 @@
#include "charsets.h" #include "charsets.h"
#include "resize.h" #include "resize.h"
#include <structmember.h> #include <structmember.h>
#include <sys/mman.h>
#include "../3rdparty/ringbuf/ringbuf.h" #include "../3rdparty/ringbuf/ringbuf.h"
extern PyTypeObject Line_Type; extern PyTypeObject Line_Type;
@@ -22,22 +23,27 @@ add_segment(HistoryBuf *self, index_type num) {
const size_t cpu_cells_size = self->xnum * SEGMENT_SIZE * sizeof(CPUCell); const size_t cpu_cells_size = self->xnum * SEGMENT_SIZE * sizeof(CPUCell);
const size_t gpu_cells_size = self->xnum * SEGMENT_SIZE * sizeof(GPUCell); const size_t gpu_cells_size = self->xnum * SEGMENT_SIZE * sizeof(GPUCell);
const size_t segment_size = cpu_cells_size + gpu_cells_size + SEGMENT_SIZE * sizeof(LineAttrs); const size_t segment_size = cpu_cells_size + gpu_cells_size + SEGMENT_SIZE * sizeof(LineAttrs);
char *mem = calloc(num, segment_size); if (num > SIZE_MAX / segment_size) fatal("History buffer segment allocation is too large");
if (!mem) fatal("Out of memory allocating new history buffer segment"); const size_t mmap_size = num * segment_size;
char *mem = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
if (mem == MAP_FAILED) fatal("Out of memory allocating new history buffer segment");
char *needs_free = mem; char *needs_free = mem;
for (HistoryBufSegment *s = self->segments + self->num_segments; s < self->segments + self->num_segments + num; s++, mem += segment_size) { for (HistoryBufSegment *s = self->segments + self->num_segments; s < self->segments + self->num_segments + num; s++, mem += segment_size) {
s->cpu_cells = (CPUCell*)mem; s->cpu_cells = (CPUCell*)mem;
s->gpu_cells = (GPUCell*)(((uint8_t*)s->cpu_cells) + cpu_cells_size); s->gpu_cells = (GPUCell*)(((uint8_t*)s->cpu_cells) + cpu_cells_size);
s->line_attrs = (LineAttrs*)(((uint8_t*)s->gpu_cells) + gpu_cells_size); s->line_attrs = (LineAttrs*)(((uint8_t*)s->gpu_cells) + gpu_cells_size);
s->mem = NULL; s->mem = NULL;
s->mmap_size = 0;
} }
self->segments[self->num_segments].mem = needs_free; self->segments[self->num_segments].mem = needs_free;
self->segments[self->num_segments].mmap_size = mmap_size;
self->num_segments += num; self->num_segments += num;
} }
static void static void
free_segment(HistoryBufSegment *s) { free_segment(HistoryBufSegment *s) {
free(s->mem); zero_at_ptr(s); if (s->mem && munmap(s->mem, s->mmap_size) != 0) log_error("Failed to unmap history buffer segment: %s", strerror(errno));
zero_at_ptr(s);
} }
static index_type static index_type

1
kitty/history.h
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@@ -14,6 +14,7 @@ typedef struct {
CPUCell *cpu_cells; CPUCell *cpu_cells;
LineAttrs *line_attrs; LineAttrs *line_attrs;
void *mem; void *mem;
size_t mmap_size;
} HistoryBufSegment; } HistoryBufSegment;
typedef struct { typedef struct {