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Date:   Fri, 4 Nov 2022 16:53:13 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Minchan Kim <minchan@kernel.org>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nitin Gupta <ngupta@vflare.org>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCHv4 4/9] zram: Introduce recompress sysfs knob
Message-ID: <Y2TE6XSTkyXVF+kB@google.com>
References: <20221018045533.2396670-1-senozhatsky@chromium.org>
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 <Y2Lbxp6to4QNYyGe@google.com>
 <Y2M0t5etyJiUfeQi@google.com>
 <Y2PzseskzPelrZum@google.com>
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On (22/11/03 10:00), Minchan Kim wrote:
> zram->table[index].flags
> 
> If we squeeze the algorithm index, we could work like this
> without ZRAM_RECOMP_SKIP.

Something like this?

Allocate two ->flags bits for priority and one bit for RECOMP_SKIP.
Two priority bits let us to have 3 alternative algorithms (01 10 11)
plus one default (00). So 4 in total.

---
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 12f03745baf9..af0ff58087ca 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -127,6 +127,19 @@ static size_t zram_get_obj_size(struct zram *zram, u32 index)
        return zram->table[index].flags & (BIT(ZRAM_FLAG_SHIFT) - 1);
 }
 
+static inline void zram_set_priority(struct zram *zram, u32 index, u32 prio)
+{
+       prio &= ZRAM_COMP_PRIORITY_MASK;
+       zram->table[index].flags &= (prio << ZRAM_COMP_PRIORITY_1);
+}
+
+static inline u32 zram_get_priority(struct zram *zram, u32 index)
+{
+       u32 prio = zram->table[index].flags;
+
+       return prio & ZRAM_COMP_PRIORITY_MASK;
+}
+
 static void zram_set_obj_size(struct zram *zram,
                                        u32 index, size_t size)
 {
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index bdfc9bf0bdd5..33e52c5a9a90 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -40,6 +40,8 @@
  */
 #define ZRAM_FLAG_SHIFT (PAGE_SHIFT + 1)
 
+#define ZRAM_COMP_PRIORITY_MASK  0x3
+
 /* Flags for zram pages (table[page_no].flags) */
 enum zram_pageflags {
        /* zram slot is locked */
@@ -49,8 +51,9 @@ enum zram_pageflags {
        ZRAM_UNDER_WB,  /* page is under writeback */
        ZRAM_HUGE,      /* Incompressible page */
        ZRAM_IDLE,      /* not accessed page since last idle marking */
-       ZRAM_RECOMP,    /* page was recompressed */
        ZRAM_RECOMP_SKIP, /* secondary algorithm cannot compress this page */
+       ZRAM_COMP_PRIORITY_1,
+       ZRAM_COMP_PRIORITY_2,
 
        __NR_ZRAM_PAGEFLAGS,
 };