If we were using a ProcessPagingScope to temporarily go into another
process's page tables, things would fall apart when hitting a kernel
NP fault, since we'd clone the kernel page directory entry into the
*currently active process's* page directory rather than cloning it
into the *currently active* page directory.
Instead of generating ByteBuffers and keeping those lying around, have
these filesystems generate KBuffers instead. These are way less spooky
to leave around for a while.
Since FileDescription will keep a generated file buffer around until
userspace has read the whole thing, this prevents trivially exhausting
the kmalloc heap by opening many files in /proc for example.
The code responsible for generating each /proc file is not perfectly
efficient and many of them still use ByteBuffers internally but they
at least go away when we return now. :^)
Generate a special page containing the "return from signal" trampoline code
on startup and then route signalled threads to it. This avoids a page
allocation in every process that ever receives a signal.
Region now has is_user_accessible(), which informs the memory manager how
to map these pages. Previously, we were just passing a "bool user_allowed"
to various functions and I'm not at all sure that any of that was correct.
All the Region constructors are now hidden, and you must go through one of
these helpers to construct a region:
- Region::create_user_accessible(...)
- Region::create_kernel_only(...)
That ensures that we don't accidentally create a Region without specifying
user accessibility. :^)
I was messing around with this to tell the compiler that these functions
always return the same value no matter how many times you call them.
It doesn't really seem to improve code generation and it looks weird so
let's just get rid of it.
This is obviously more readable. If we ever run into a situation where
ref count churn is actually causing trouble in the future, we can deal with
it then. For now, let's keep it simple. :^)
If we get an NP page fault in a process, and the fault address is in the
kernel address range (anywhere above 0xc0000000), we probably just need
to copy the page table info over from the kernel page directory.
The kernel doesn't allocate address space until it's needed, and when it
does allocate some, it only puts the info in the kernel page directory,
and any *new* page directories created from that point on. Existing page
directories need to be updated, and that's what this patch fixes.
Instead of PDE's and PTE's being weird wrappers around dword*, just have
MemoryManager::ensure_pte() return a PageDirectoryEntry&, which in turn has
a PageTableEntry* entries().
I've been trying to understand how things ended up this way, and I suspect
it was because I inadvertently invoked the PageDirectoryEntry copy ctor in
the original work on this, which must have made me very confused..
Anyways, now things are a bit saner and we can move forward towards a better
future, etc. :^)
This method is used in BXVGADevice to create pages for the framebuffer;
we should neither make the PhysicalPage instances eternal, nor hand over
actual physical pages to the memory allocator.
After PhysicalPage::return_to_freelist(), an actual physical page
is returned back to the memory manager; which will create a new
PhysicalPage instance if it decides to reuse the physical page. This
means this PhysicalPage instance should be freed; otherwise it would
get leaked.
This makes no functional difference, but it makes it clear that
MemoryManager and PhysicalRegion take over the actual physical
page represented by this PhysicalPage instance.
Pages created with PhysicalPage::create_eternal() should *not* be
returnable to the freelist; and pages created with the regular
PhysicalPage::create() should be; not the other way around.
This significantly reduces the pressure on the kernel heap when
allocating a lot of pages.
Previously at about 250MB allocated, the free page list would outgrow
the kernel's heap. Given that there is no longer a page list, this does
not happen.
The next barrier will be the kernel memory used by the page records for
in-use memory. This kicks in at about 1GB.
This makes it possible to run Serenity with more than 64 MB of RAM.
Because each physical page is represented by a PhysicalPage object, and such
objects are allocated using kmalloc_eternal(), more RAM means more pressure
on kmalloc_eternal(), so we're gonna need a better strategy for this.
But for now, let's just celebrate that we can use the 128 MB of RAM we've
been telling QEMU to run with. :^)
String&& is just not very practical. Also return const String& when the
returned string is a member variable. The call site is free to make a copy
if he wants, but otherwise we can avoid the retain count churn.
Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.
Since we transition to a new PageDirectory on exec(), we need a matching
RangeAllocator to go with the new directory. Instead of juggling this in
Process and MemoryManager, simply attach the RangeAllocator to the
PageDirectory instead.
Fixes#61.
This replaces the previous virtual address allocator which was basically
just "m_next_address += size;"
With this in place, virtual addresses can get reused, which cuts down on
the number of page tables created. When we implement ASLR some day, we'll
probably have to do page table deallocation, but for now page tables are
only deallocated once the process dies.
This means that kernel regions will eagerly get physical pages allocated.
It would be nice to zero-fill these on demand instead, but that would
require a bunch of MemoryManager changes.
This patch moves away from using kmalloc memory for thread kernel stacks.
This reduces pressure on kmalloc (16 KB per thread adds up fast) and
prevents kernel stack overflow from scribbling all over random unrelated
kernel memory.
