android/android_kernel_samsung_sm8650
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

ANDROID: mm: cma: retry allocations in cma_alloc

Browse Source 
CMA allocations will fail if 'pinned' pages are in a CMA area, since
we cannot migrate pinned pages. The _refcount of a struct page being
greater than _mapcount for that page can cause pinning for anonymous
pages.  This is because try_to_unmap(), which (1) is called in the CMA
allocation path, and (2) decrements both _refcount and _mapcount for a
page, will stop unmapping a page from VMAs once the _mapcount for a
page reaches 0.  This implies that after try_to_unmap() has finished
successfully for a page where _recount > _mapcount, that _refcount
will be greater than 0.  Later in the CMA allocation path in
migrate_page_move_mapping(), we will have one more reference count
than intended for anonymous pages, meaning the allocation will fail
for that page.

One example of where _refcount can be greater than _mapcount for a
page we would not expect to be pinned is inside of copy_one_pte(),
which is called during a fork. For ptes for which pte_present(pte) ==
true, copy_one_pte() will increment the _refcount field followed by
the  _mapcount field of a page. If the process doing copy_one_pte() is
context switched out after incrementing _refcount but before
incrementing _mapcount, then the page will be temporarily pinned.

So, inside of cma_alloc(), instead of giving up when
alloc_contig_range() returns -EBUSY after having scanned a whole
CMA-region bitmap, perform retries with sleeps to give the system an
opportunity to unpin any pinned pages.

Additionally, based off feedback by Minchan Kim, add the ability to
exit early if a fatal signal is pending (this is a delta from the
mailing-list version of this patch).

Bug: 168521646
Link: https://lore.kernel.org/lkml/1596682582-29139-2-git-send-email-cgoldswo@codeaurora.org/
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>
Co-developed-by: Susheel Khiani <skhiani@codeaurora.org>
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>
Co-developed-by: Vinayak Menon <vinmenon@codeaurora.org>
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
Change-Id: I2f0c8388f9163e0decd631d9ae07bb6ad9ab79c8
This commit is contained in:
Chris Goldsworthy 2020-09-18 09:19:53 -07:00
parent 50f98784b1
commit 73eda8ec74
1 changed files with 26 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
mm/cma.c
View File

@ -33,6 +33,8 @@
#include <linux/highmem.h>
#include <linux/io.h>
#include <linux/kmemleak.h>
#include <linux/sched.h>
#include <linux/jiffies.h>
#include <trace/events/cma.h>
#include "cma.h"
@ -420,6 +422,8 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
size_t i;
struct page *page = NULL;
int ret = -ENOMEM;
int num_attempts = 0;
int max_retries = 5;
if (!cma || !cma->count || !cma->bitmap)
return NULL;
@ -444,8 +448,28 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
bitmap_maxno, start, bitmap_count, mask,
offset);
if (bitmap_no >= bitmap_maxno) {
mutex_unlock(&cma->lock);
break;
if ((num_attempts < max_retries) && (ret == -EBUSY)) {
mutex_unlock(&cma->lock);
if (fatal_signal_pending(current))
break;
/*
* Page may be momentarily pinned by some other
* process which has been scheduled out, e.g.
* in exit path, during unmap call, or process
* fork and so cannot be freed there. Sleep
* for 100ms and retry the allocation.
*/
start = 0;
ret = -ENOMEM;
schedule_timeout_killable(msecs_to_jiffies(100));
num_attempts++;
continue;
} else {
mutex_unlock(&cma->lock);
break;
}
}
bitmap_set(cma->bitmap, bitmap_no, bitmap_count);
/*