staging: erofs: refine compressed pages preload flow

Currently, there are two kinds of compressed pages in erofs:
  1) file pages for the in-place decompression and
  2) managed pages for cached decompression.
Both are all stored in grp->compressed_pages[].

For managed pages, they could already exist or could be preloaded
in this round, including the following cases in detail:
  1) Already valid (loaded in some previous round);
  2) PAGE_UNALLOCATED, should be allocated at the time of submission;
  3) Just found in the managed cache, and with an extra page ref.
Currently, 1) and 3) can be distinguishable by lock_page and
checking its PG_private, which is guaranteed by the reclaim path,
but it's better to do a double check by using an extra tag.

This patch reworks the preload flow by introducing such the tag
by using tagged pointer, too many #ifdefs are removed as well.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/erofs/unzip_vle.c b/drivers/staging/erofs/unzip_vle.c
index de41f7b739ac5dfdc975d83455e087f6c4ed6930..2b494f29e2c2d8ecf351b4021a488331864d1154 100644 (file)
--- a/drivers/staging/erofs/unzip_vle.c
+++ b/drivers/staging/erofs/unzip_vle.c
@@ -21,6 +21,21 @@
  */
 #define PAGE_UNALLOCATED     ((void *)0x5F0E4B1D)
 
+/* how to allocate cached pages for a workgroup */
+enum z_erofs_cache_alloctype {
+       DONTALLOC,      /* don't allocate any cached pages */
+       DELAYEDALLOC,   /* delayed allocation (at the time of submitting io) */
+};
+
+/*
+ * tagged pointer with 1-bit tag for all compressed pages
+ * tag 0 - the page is just found with an extra page reference
+ */
+typedef tagptr1_t compressed_page_t;
+
+#define tag_compressed_page_justfound(page) \
+       tagptr_fold(compressed_page_t, page, 1)
+
 static struct workqueue_struct *z_erofs_workqueue __read_mostly;
 static struct kmem_cache *z_erofs_workgroup_cachep __read_mostly;
 
@@ -131,38 +146,58 @@ struct z_erofs_vle_work_builder {
        { .work = NULL, .role = Z_EROFS_VLE_WORK_PRIMARY_FOLLOWED }
 
 #ifdef EROFS_FS_HAS_MANAGED_CACHE
-
-static bool grab_managed_cache_pages(struct address_space *mapping,
-                                    erofs_blk_t start,
-                                    struct page **compressed_pages,
-                                    int clusterblks,
-                                    bool reserve_allocation)
+static void preload_compressed_pages(struct z_erofs_vle_work_builder *bl,
+                                    struct address_space *mc,
+                                    pgoff_t index,
+                                    unsigned int clusterpages,
+                                    enum z_erofs_cache_alloctype type,
+                                    struct list_head *pagepool,
+                                    gfp_t gfp)
 {
-       bool noio = true;
-       unsigned int i;
+       struct page **const pages = bl->compressed_pages;
+       const unsigned int remaining = bl->compressed_deficit;
+       bool standalone = true;
+       unsigned int i, j = 0;
+
+       if (bl->role < Z_EROFS_VLE_WORK_PRIMARY_FOLLOWED)
+               return;
+
+       gfp = mapping_gfp_constraint(mc, gfp) & ~__GFP_RECLAIM;
 
-       /* TODO: optimize by introducing find_get_pages_range */
-       for (i = 0; i < clusterblks; ++i) {
-               struct page *page, *found;
+       index += clusterpages - remaining;
 
-               if (READ_ONCE(compressed_pages[i]))
+       for (i = 0; i < remaining; ++i) {
+               struct page *page;
+               compressed_page_t t;
+
+               /* the compressed page was loaded before */
+               if (READ_ONCE(pages[i]))
                        continue;
 
-               page = found = find_get_page(mapping, start + i);
-               if (!found) {
-                       noio = false;
-                       if (!reserve_allocation)
-                               continue;
-                       page = PAGE_UNALLOCATED;
+               page = find_get_page(mc, index + i);
+
+               if (page) {
+                       t = tag_compressed_page_justfound(page);
+               } else if (type == DELAYEDALLOC) {
+                       t = tagptr_init(compressed_page_t, PAGE_UNALLOCATED);
+               } else {        /* DONTALLOC */
+                       if (standalone)
+                               j = i;
+                       standalone = false;
+                       continue;
                }
 
-               if (!cmpxchg(compressed_pages + i, NULL, page))
+               if (!cmpxchg_relaxed(&pages[i], NULL, tagptr_cast_ptr(t)))
                        continue;
 
-               if (found)
-                       put_page(found);
+               if (page)
+                       put_page(page);
        }
-       return noio;
+       bl->compressed_pages += j;
+       bl->compressed_deficit = remaining - j;
+
+       if (standalone)
+               bl->role = Z_EROFS_VLE_WORK_PRIMARY;
 }
 
 /* called by erofs_shrinker to get rid of all compressed_pages */
@@ -234,6 +269,17 @@ int erofs_try_to_free_cached_page(struct address_space *mapping,
        }
        return ret;
 }
+#else
+static void preload_compressed_pages(struct z_erofs_vle_work_builder *bl,
+                                    struct address_space *mc,
+                                    pgoff_t index,
+                                    unsigned int clusterpages,
+                                    enum z_erofs_cache_alloctype type,
+                                    struct list_head *pagepool,
+                                    gfp_t gfp)
+{
+       /* nowhere to load compressed pages from */
+}
 #endif
 
 /* page_type must be Z_EROFS_PAGE_TYPE_EXCLUSIVE */
@@ -608,6 +654,26 @@ struct z_erofs_vle_frontend {
        .owned_head = Z_EROFS_VLE_WORKGRP_TAIL, \
        .backmost = true, }
 
+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+static inline bool
+should_alloc_managed_pages(struct z_erofs_vle_frontend *fe, erofs_off_t la)
+{
+       if (fe->backmost)
+               return true;
+
+       if (EROFS_FS_ZIP_CACHE_LVL >= 2)
+               return la < fe->headoffset;
+
+       return false;
+}
+#else
+static inline bool
+should_alloc_managed_pages(struct z_erofs_vle_frontend *fe, erofs_off_t la)
+{
+       return false;
+}
+#endif
+
 static int z_erofs_do_read_page(struct z_erofs_vle_frontend *fe,
                                struct page *page,
                                struct list_head *page_pool)
@@ -622,12 +688,7 @@ static int z_erofs_do_read_page(struct z_erofs_vle_frontend *fe,
        bool tight = builder_is_followed(builder);
        struct z_erofs_vle_work *work = builder->work;
 
-#ifdef EROFS_FS_HAS_MANAGED_CACHE
-       struct address_space *const mc = MNGD_MAPPING(sbi);
-       struct z_erofs_vle_workgroup *grp;
-       bool noio_outoforder;
-#endif
-
+       enum z_erofs_cache_alloctype cache_strategy;
        enum z_erofs_page_type page_type;
        unsigned int cur, end, spiltted, index;
        int err = 0;
@@ -667,20 +728,16 @@ repeat:
        if (unlikely(err))
                goto err_out;
 
-#ifdef EROFS_FS_HAS_MANAGED_CACHE
-       grp = fe->builder.grp;
-
-       /* let's do out-of-order decompression for noio */
-       noio_outoforder = grab_managed_cache_pages(mc,
-               erofs_blknr(map->m_pa),
-               grp->compressed_pages, erofs_blknr(map->m_plen),
-               /* compressed page caching selection strategy */
-               fe->backmost | (EROFS_FS_ZIP_CACHE_LVL >= 2 ?
-                               map->m_la < fe->headoffset : 0));
-
-       if (noio_outoforder && builder_is_followed(builder))
-               builder->role = Z_EROFS_VLE_WORK_PRIMARY;
-#endif
+       /* preload all compressed pages (maybe downgrade role if necessary) */
+       if (should_alloc_managed_pages(fe, map->m_la))
+               cache_strategy = DELAYEDALLOC;
+       else
+               cache_strategy = DONTALLOC;
+
+       preload_compressed_pages(builder, MNGD_MAPPING(sbi),
+                                map->m_pa / PAGE_SIZE,
+                                map->m_plen / PAGE_SIZE,
+                                cache_strategy, page_pool, GFP_KERNEL);
 
        tight &= builder_is_followed(builder);
        work = builder->work;
@@ -1062,6 +1119,9 @@ pickup_page_for_submission(struct z_erofs_vle_workgroup *grp,
        struct address_space *mapping;
        struct page *oldpage, *page;
 
+       compressed_page_t t;
+       int justfound;
+
 repeat:
        page = READ_ONCE(grp->compressed_pages[nr]);
        oldpage = page;
@@ -1078,6 +1138,11 @@ repeat:
                goto out_allocpage;
        }
 
+       /* process the target tagged pointer */
+       t = tagptr_init(compressed_page_t, page);
+       justfound = tagptr_unfold_tags(t);
+       page = tagptr_unfold_ptr(t);
+
        mapping = READ_ONCE(page->mapping);
 
        /*
@@ -1085,7 +1150,10 @@ repeat:
         * get such a cached-like page.
         */
        if (nocache) {
-               /* should be locked, not uptodate, and not truncated */
+               /* if managed cache is disabled, it is impossible `justfound' */
+               DBG_BUGON(justfound);
+
+               /* and it should be locked, not uptodate, and not truncated */
                DBG_BUGON(!PageLocked(page));
                DBG_BUGON(PageUptodate(page));
                DBG_BUGON(!mapping);
@@ -1102,11 +1170,22 @@ repeat:
 
        lock_page(page);
 
+       /* only true if page reclaim goes wrong, should never happen */
+       DBG_BUGON(justfound && PagePrivate(page));
+
        /* the page is still in manage cache */
        if (page->mapping == mc) {
                WRITE_ONCE(grp->compressed_pages[nr], page);
 
                if (!PagePrivate(page)) {
+                       /*
+                        * impossible to be !PagePrivate(page) for
+                        * the current restriction as well if
+                        * the page is already in compressed_pages[].
+                        */
+                       DBG_BUGON(!justfound);
+
+                       justfound = 0;
                        set_page_private(page, (unsigned long)grp);
                        SetPagePrivate(page);
                }
@@ -1124,6 +1203,7 @@ repeat:
         * reuse this one, let's allocate a new cache-managed page.
         */
        DBG_BUGON(page->mapping);
+       DBG_BUGON(!justfound);
 
        tocache = true;
        unlock_page(page);