Fix page allocation failure in kcalloc by converting the large 1-dimensional
array into a 2-dimensional array of order-0 (4KB) pages. This eliminates the
need for non-order-0 allocations, improving allocation reliability under memory
pressure. The 2D array ensures virtual contiguity for the caller maintaining
functional equivalence.

Related to #VSTOR-112413
https://virtuozzo.atlassian.net/browse/VSTOR-112413

Signed-off-by: Liu Kui <kui....@virtuozzo.com>
---
 fs/fuse/kio/pcs/pcs_mr.c | 55 +++++++++++++++++++++++++---------------
 fs/fuse/kio/pcs/pcs_mr.h | 21 ++++++++++-----
 2 files changed, 50 insertions(+), 26 deletions(-)

diff --git a/fs/fuse/kio/pcs/pcs_mr.c b/fs/fuse/kio/pcs/pcs_mr.c
index cbd3b440dd1b..8e1dbc1121ce 100644
--- a/fs/fuse/kio/pcs/pcs_mr.c
+++ b/fs/fuse/kio/pcs/pcs_mr.c
@@ -13,11 +13,18 @@
 void pcs_umem_release(struct pcs_umem *umem)
 {
        struct mm_struct *mm_s = umem->mm;
+       int i, npages = umem->npages;
 
-       unpin_user_pages(umem->pages, umem->npages);
+       for (i = 0; npages; i++) {
+               int to_free = min_t(int, PCS_PAGES_PER_CHUNK, npages);
+
+               unpin_user_pages(umem->page_chunk[i].pages, to_free);
+               kfree(umem->page_chunk[i].pages);
+               npages -= to_free;
+       }
        atomic64_sub(umem->npages, &mm_s->pinned_vm);
        mmdrop(mm_s);
-       kfree(umem->pages);
+       kfree(umem->page_chunk);
        kfree(umem);
 }
 
@@ -27,14 +34,13 @@ void pcs_umem_release(struct pcs_umem *umem)
 struct pcs_umem *pcs_umem_get(u64 start, u64 len)
 {
        struct pcs_umem *umem = NULL;
-       struct page **pages;
-       int npages;
-       u64 fp_va;
        struct mm_struct *mm_s;
-       int got, ret;
+       u64 fp_va;
+       int npages, nchunks, i, ret;
 
        fp_va = start & PAGE_MASK;
        npages = PAGE_ALIGN(start + len - fp_va) >> PAGE_SHIFT;
+       nchunks = (npages >> PCS_PAGE_CHUNK_SHIFT) + 1;
 
        umem = kzalloc(sizeof(*umem), GFP_KERNEL);
        if (!umem)
@@ -48,25 +54,34 @@ struct pcs_umem *pcs_umem_get(u64 start, u64 len)
        mmap_read_lock(mm_s);
 
        umem->fp_addr = fp_va;
-       umem->pages = kcalloc(npages, sizeof(struct page *), GFP_KERNEL);
-       if (!umem->pages) {
+       umem->page_chunk = kcalloc(nchunks, sizeof(struct pcs_page_chunk *), 
GFP_KERNEL);
+       if (!umem->page_chunk) {
                ret = -ENOMEM;
                goto out_err;
        }
 
-       got = 0;
-       while (npages) {
-               pages = &umem->pages[got];
-               ret = pin_user_pages(fp_va, npages, FOLL_WRITE | FOLL_LONGTERM, 
pages, NULL);
-               if (ret < 0)
-                       goto out_err;
+       for (i = 0; npages; i++) {
+               int n = min_t(int, npages, PCS_PAGES_PER_CHUNK);
+               struct page **pages = kcalloc(n, sizeof(struct page *), 
GFP_KERNEL);
 
-               WARN_ON(ret == 0);
-               umem->npages += ret;
-               atomic64_add(ret, &mm_s->pinned_vm);
-               fp_va += ret * PAGE_SIZE;
-               npages -= ret;
-               got += ret;
+               if (!pages) {
+                       ret = -ENOMEM;
+                       goto out_err;
+               }
+               umem->page_chunk[i].pages = pages;
+
+               while (n) {
+                       ret = pin_user_pages(fp_va, n, FOLL_WRITE | 
FOLL_LONGTERM, pages, NULL);
+                       if (ret < 0)
+                               goto out_err;
+
+                       atomic64_add(ret, &mm_s->pinned_vm);
+                       umem->npages += ret;
+                       fp_va += ret * PAGE_SIZE;
+                       pages += ret;
+                       n -= ret;
+                       npages -= ret;
+               }
        }
        mmap_read_unlock(mm_s);
 
diff --git a/fs/fuse/kio/pcs/pcs_mr.h b/fs/fuse/kio/pcs/pcs_mr.h
index dae9931d9967..64f237f57dec 100644
--- a/fs/fuse/kio/pcs/pcs_mr.h
+++ b/fs/fuse/kio/pcs/pcs_mr.h
@@ -11,6 +11,8 @@
 struct pcs_umem;
 
 #define PCS_MAX_MR             0x10000
+#define PCS_PAGE_CHUNK_SHIFT 9
+#define PCS_PAGES_PER_CHUNK (1 << PCS_PAGE_CHUNK_SHIFT)
 
 struct pcs_mr_set {
        struct xarray   mr_xa;  /* array of registered MRs*/
@@ -18,10 +20,15 @@ struct pcs_mr_set {
        atomic_t        mr_num;         /* number of registered MRs*/
 };
 
+struct pcs_page_chunk
+{
+       struct page **pages; /* array of pinned pages */
+};
+
 struct pcs_umem {
-       u64     fp_addr;        /* First page base address */
-       int     npages;         /* number of pinned pages */
-       struct page     **pages;        /* array of pinned pages */
+       struct pcs_page_chunk *page_chunk;
+       int npages; /* number of pinned pages */
+       u64 fp_addr; /* First page base address */
        struct mm_struct *mm;   /* mm the memory belongs to */
 };
 
@@ -40,10 +47,12 @@ struct pcs_mr {
  */
 static inline struct page *pcs_umem_page(struct pcs_umem *umem, u64 addr)
 {
-       unsigned int idx = (addr - umem->fp_addr) >> PAGE_SHIFT;
+       unsigned int page_idx = (addr - umem->fp_addr) >> PAGE_SHIFT;
+       unsigned int chunk_idx = page_idx >> PCS_PAGE_CHUNK_SHIFT;
+       unsigned int page_in_chunk = page_idx & (PCS_PAGES_PER_CHUNK - 1);
 
-       if (likely(idx < umem->npages))
-               return umem->pages[idx];
+       if (likely(page_idx < umem->npages))
+               return umem->page_chunk[chunk_idx].pages[page_in_chunk];
        return NULL;
 }
 
-- 
2.39.5 (Apple Git-154)

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