On Fri, Nov 13, 2020 at 03:42:25PM -0800, Roman Gushchin wrote:

вт, 10 нояб. 2020 г. в 07:16, Mike Rapoport [off-list ref]:

quoted

From: Mike Rapoport <redacted>

Account memory consumed by secretmem to memcg. The accounting is updated
when the memory is actually allocated and freed.

Signed-off-by: Mike Rapoport <redacted>
---
 mm/filemap.c   |  2 +-
 mm/secretmem.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 249cf489f5df..11387a077373 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c

@@ -844,7 +844,7 @@ static noinline int __add_to_page_cache_locked(struct page *page,
        page->mapping = mapping;
        page->index = offset;

-       if (!huge) {
+       if (!huge && !page->memcg_data) {
                error = mem_cgroup_charge(page, current->mm, gfp);
                if (error)
                        goto error;

diff --git a/mm/secretmem.c b/mm/secretmem.c
index 1aa2b7cffe0d..1eb7667016fa 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c

@@ -17,6 +17,7 @@
 #include <linux/syscalls.h>
 #include <linux/memblock.h>
 #include <linux/pseudo_fs.h>
+#include <linux/memcontrol.h>
 #include <linux/set_memory.h>
 #include <linux/sched/signal.h>

@@ -49,6 +50,38 @@ struct secretmem_ctx {

 static struct cma *secretmem_cma;

Hi Mike!

quoted

+static int secretmem_memcg_charge(struct page *page, gfp_t gfp, int order)
+{
+       unsigned long nr_pages = (1 << order);
+       int i, err;
+
+       err = memcg_kmem_charge_page(page, gfp, order);
+       if (err)
+               return err;
+
+       for (i = 1; i < nr_pages; i++) {
+               struct page *p = page + i;
+
+               p->memcg_data = page->memcg_data;
+       }

Hm, it looks very strange to me. Why do we need to copy memcg_data?
What about css reference counting?

I need to copy memcg_data to mark a page as being accounted so it won't
be charged again when it is added to page cache.

What happens here is that I allocate a large page and then use it as a
local cache for allocations in secretmem_fault(). I charge the large
page as kmem. 

During secretmem_fault() a small sub-page from that large page goes into
page cache and there I skip its memcg accounting.

In the end, when the large page is freed, the memcg_data for all its
sub-pages is cleared and I uncharge memcg with the order of large page.

An alternative would be to uncharge a small page from kmem in
secretmem_fault() and make this page charged in add_to_page_cache(), but
that would complicate the release path as I would need to re-charge the
small page back to kmem at secretmem_freepage() and track all the
participating memcgs till the large page is freed.

And what about statistics?

Hmm, that's probably won't be accurate :-/

I'm sorry for being late.

Thank you!

quoted

+
+       return 0;
+}
+
+static void secretmem_memcg_uncharge(struct page *page, int order)
+{
+       unsigned long nr_pages = (1 << order);
+       int i;
+
+       for (i = 1; i < nr_pages; i++) {
+               struct page *p = page + i;
+
+               p->memcg_data = 0;
+       }
+
+       memcg_kmem_uncharge_page(page, PMD_PAGE_ORDER);
+}
+
 static int secretmem_pool_increase(struct secretmem_ctx *ctx, gfp_t gfp)
 {
        unsigned long nr_pages = (1 << PMD_PAGE_ORDER);

@@ -61,10 +94,14 @@ static int secretmem_pool_increase(struct secretmem_ctx *ctx, gfp_t gfp)
        if (!page)
                return -ENOMEM;

-       err = set_direct_map_invalid_noflush(page, nr_pages);
+       err = secretmem_memcg_charge(page, gfp, PMD_PAGE_ORDER);
        if (err)
                goto err_cma_release;

+       err = set_direct_map_invalid_noflush(page, nr_pages);
+       if (err)
+               goto err_memcg_uncharge;
+
        addr = (unsigned long)page_address(page);
        err = gen_pool_add(pool, addr, PMD_SIZE, NUMA_NO_NODE);
        if (err)

@@ -81,6 +118,8 @@ static int secretmem_pool_increase(struct secretmem_ctx *ctx, gfp_t gfp)
         * won't fail
         */
        set_direct_map_default_noflush(page, nr_pages);
+err_memcg_uncharge:
+       secretmem_memcg_uncharge(page, PMD_PAGE_ORDER);
 err_cma_release:
        cma_release(secretmem_cma, page, nr_pages);
        return err;

@@ -310,6 +349,7 @@ static void secretmem_cleanup_chunk(struct gen_pool *pool,
        int i;

        set_direct_map_default_noflush(page, nr_pages);
+       secretmem_memcg_uncharge(page, PMD_PAGE_ORDER);

        for (i = 0; i < nr_pages; i++)
                clear_highpage(page + i);
--

2.28.0

-- 
Sincerely yours,
Mike.