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Kernel: Start implementing purgeable memory support

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It's now possible to get purgeable memory by using mmap(MAP_PURGEABLE).
Purgeable memory has a "volatile" flag that can be set using madvise():

- madvise(..., MADV_SET_VOLATILE)
- madvise(..., MADV_SET_NONVOLATILE)

When in the "volatile" state, the kernel may take away the underlying
physical memory pages at any time, without notifying the owner.
This gives you a guilt discount when caching very large things. :^)

Setting a purgeable region to non-volatile will return whether or not
the memory has been taken away by the kernel while being volatile.
Basically, if madvise(..., MADV_SET_NONVOLATILE) returns 1, that means
the memory was purged while volatile, and whatever was in that piece
of memory needs to be reconstructed before use.
This commit is contained in:
Andreas Kling 2019-12-09 19:12:38 +01:00
parent 7248c34e35
commit dbb644f20c
13 changed files with 196 additions and 9 deletions
Download patch file Download diff file Expand all files Collapse all files

7
Libraries/LibC/mman.cpp
View file

@ -56,4 +56,11 @@ int shm_unlink(const char* name)
int rc = syscall(SC_shm_unlink, name);
__RETURN_WITH_ERRNO(rc, rc, -1);
}
int madvise(void* address, size_t size, int advice)
{
int rc = syscall(SC_madvise, address, size, advice);
__RETURN_WITH_ERRNO(rc, rc, -1);
}
}

5
Libraries/LibC/mman.h
View file

@ -9,6 +9,7 @@
#define MAP_ANONYMOUS 0x20
#define MAP_ANON MAP_ANONYMOUS
#define MAP_STACK 0x40
#define MAP_PURGEABLE 0x80
#define PROT_READ 0x1
#define PROT_WRITE 0x2
@ -17,6 +18,9 @@
#define MAP_FAILED ((void*)-1)
#define MADV_SET_VOLATILE 0x100
#define MADV_SET_NONVOLATILE 0x200
__BEGIN_DECLS
void* mmap(void* addr, size_t, int prot, int flags, int fd, off_t);
@ -26,5 +30,6 @@ int mprotect(void*, size_t, int prot);
int set_mmap_name(void*, size_t, const char*);
int shm_open(const char* name, int flags, mode_t);
int shm_unlink(const char* name);
int madvise(void*, size_t, int advice);
__END_DECLS