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Kernel: Remove MAP_PURGEABLE from mmap

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This brings mmap more in line with other operating systems. Prior to
this, it was impossible to request memory that was definitely committed,
instead MAP_PURGEABLE would provide a region that was not actually
purgeable, but also not fully committed, which meant that using such memory
still could cause crashes when the underlying pages could no longer be
allocated.

This fixes some random crashes in low-memory situations where non-volatile
memory is mapped (e.g. malloc, tls, Gfx::Bitmap, etc) but when a page in
these regions is first accessed, there is insufficient physical memory
available to commit a new page.
This commit is contained in:
Tom 2020-09-04 11:47:49 -06:00 • committed by Andreas Kling
parent c3451899bc
commit e21cc4cff6
6 changed files with 12 additions and 20 deletions
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10
Libraries/LibGfx/Bitmap.cpp
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@ -437,13 +437,13 @@ Optional<BackingStore> Bitmap::allocate_backing_store(BitmapFormat format, const
const auto pitch = minimum_pitch(size.width(), format);
const auto data_size_in_bytes = size_in_bytes(pitch, size.height());
void* data = nullptr;
int map_flags = MAP_ANONYMOUS | MAP_PRIVATE;
if (purgeable == Purgeable::Yes)
map_flags |= MAP_NORESERVE;
#ifdef __serenity__
int map_flags = purgeable == Purgeable::Yes ? (MAP_PURGEABLE | MAP_PRIVATE) : (MAP_ANONYMOUS | MAP_PRIVATE);
data = mmap_with_name(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0, String::format("GraphicsBitmap [%dx%d]", size.width(), size.height()).characters());
void* data = mmap_with_name(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0, String::format("GraphicsBitmap [%dx%d]", size.width(), size.height()).characters());
#else
int map_flags = (MAP_ANONYMOUS | MAP_PRIVATE);
data = mmap(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0);
void* data = mmap(nullptr, data_size_in_bytes, PROT_READ | PROT_WRITE, map_flags, 0, 0);
#endif
if (data == MAP_FAILED) {
perror("mmap");