mm: fix process_vm_rw page counts
1. There is a "-1" missing in the page number calculation in process_vm_rw_core. While this can't break anything, it can cause unnecessary allocations in certain cases: Consider handling an iovec ranging over PVM_MAX_PP_ARRAY_COUNT pages that is also aligned to a page boundary. While pp_stack could hold references to such an amount of pinned pages, nr_pages yields (PVM_MAX_PP_ARRAY + 1) in process_vm_rw_core. Consequently, a larger buffer is allocated with kmalloc for no reason. For any page boundary aligned iovec that is a multiple of PAGE_SIZE and larger than PVM_MAX_PP_ARRAY_COUNT pages, nr_pages will be too big by 1 and thus kmalloc allocates excess space for one more pointer. 2. max_pages_per_loop is constant and there is no reason to have it as a variable. A macro does the job just fine and saves memory. 3. Replaced "sizeof(struct pages *)" with "sizeof(struct page *)" to have matching types for allocation and prevent confusion. Link: https://lkml.kernel.org/r/20231111184859.44264-1-yjnworkstation@gmail.com Signed-off-by: York Jasper Niebuhr <yjnworkstation@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
parent
69e583eaca
commit
932b59e3be
|
@ -53,7 +53,10 @@ static int process_vm_rw_pages(struct page **pages,
|
|||
}
|
||||
|
||||
/* Maximum number of pages kmalloc'd to hold struct page's during copy */
|
||||
#define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
|
||||
#define PVM_MAX_KMALLOC_PAGES 2
|
||||
|
||||
/* Maximum number of pages that can be stored at a time */
|
||||
#define PVM_MAX_USER_PAGES (PVM_MAX_KMALLOC_PAGES * PAGE_SIZE / sizeof(struct page *))
|
||||
|
||||
/**
|
||||
* process_vm_rw_single_vec - read/write pages from task specified
|
||||
|
@ -79,8 +82,6 @@ static int process_vm_rw_single_vec(unsigned long addr,
|
|||
unsigned long start_offset = addr - pa;
|
||||
unsigned long nr_pages;
|
||||
ssize_t rc = 0;
|
||||
unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
|
||||
/ sizeof(struct pages *);
|
||||
unsigned int flags = 0;
|
||||
|
||||
/* Work out address and page range required */
|
||||
|
@ -92,7 +93,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
|
|||
flags |= FOLL_WRITE;
|
||||
|
||||
while (!rc && nr_pages && iov_iter_count(iter)) {
|
||||
int pinned_pages = min(nr_pages, max_pages_per_loop);
|
||||
int pinned_pages = min_t(unsigned long, nr_pages, PVM_MAX_USER_PAGES);
|
||||
int locked = 1;
|
||||
size_t bytes;
|
||||
|
||||
|
@ -171,7 +172,7 @@ static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
|
|||
iov_len = rvec[i].iov_len;
|
||||
if (iov_len > 0) {
|
||||
nr_pages_iov = ((unsigned long)rvec[i].iov_base
|
||||
+ iov_len)
|
||||
+ iov_len - 1)
|
||||
/ PAGE_SIZE - (unsigned long)rvec[i].iov_base
|
||||
/ PAGE_SIZE + 1;
|
||||
nr_pages = max(nr_pages, nr_pages_iov);
|
||||
|
@ -184,8 +185,8 @@ static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
|
|||
if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
|
||||
/* For reliability don't try to kmalloc more than
|
||||
2 pages worth */
|
||||
process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
|
||||
sizeof(struct pages *)*nr_pages),
|
||||
process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES * PAGE_SIZE,
|
||||
sizeof(struct page *)*nr_pages),
|
||||
GFP_KERNEL);
|
||||
|
||||
if (!process_pages)
|
||||
|
|
Loading…
Reference in New Issue