On Thu, Jan 14, 2021 at 7:56 PM Minchan Kim <minchan@xxxxxxxxxx> wrote:
>
> On Thu, Jan 14, 2021 at 07:40:50PM +0100, Vitaly Wool wrote:
> > On Thu, Jan 14, 2021 at 7:29 PM Minchan Kim <minchan@xxxxxxxxxx> wrote:
> > >
> > > On Fri, Dec 25, 2020 at 07:02:50PM +0800, Tian Tao wrote:
> > > > add a flag to zpool, named is "can_sleep_mapped", and have it set true
> > > > for zbud/z3fold, set false for zsmalloc. Then zswap could go the current
> > > > path if the flag is true; and if it's false, copy data from src to a
> > > > temporary buffer, then unmap the handle, take the mutex, process the
> > > > buffer instead of src to avoid sleeping function called from atomic
> > > > context.
> > > >
> > > > Signed-off-by: Tian Tao <tiantao6@xxxxxxxxxxxxx>
> > > > ---
> > > > include/linux/zpool.h | 3 +++
> > > > mm/zpool.c | 13 +++++++++++++
> > > > mm/zswap.c | 50 +++++++++++++++++++++++++++++++++++++++++++++-----
> > > > 3 files changed, 61 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/include/linux/zpool.h b/include/linux/zpool.h
> > > > index 51bf430..e899701 100644
> > > > --- a/include/linux/zpool.h
> > > > +++ b/include/linux/zpool.h
> > > > @@ -73,6 +73,7 @@ u64 zpool_get_total_size(struct zpool *pool);
> > > > * @malloc: allocate mem from a pool.
> > > > * @free: free mem from a pool.
> > > > * @shrink: shrink the pool.
> > > > + * @sleep_mapped: whether zpool driver can sleep during map.
> > >
> > > I don't think it's a good idea. It just breaks zpool abstraction
> > > in that it exposes internal implementation to user to avoid issue
> > > zswap recently introduced. It also conflicts zpool_map_handle's
> > > semantic.
> > >
> > > Rather than introducing another break in zpool due to the new
> > > zswap feature recenlty introduced, zswap could introduce
> > > CONFIG_ZSWAP_HW_COMPRESSOR. Once it's configured, zsmalloc could
> > > be disabled. And with disabling CONFIG_ZSWAP_HW_COMPRESSOR, zswap
> > > doesn't need to make any bounce buffer copy so that no existing
> > > zsmalloc user will see performance regression.
> >
> > I believe it won't help that much -- the new compressor API presumes
> > that the caller may sleep during compression and that will be an
> > accident waiting to happen as long as we use it and keep the handle
> > mapped in zsmalloc case.
> >
> > Or maybe I interpreted you wrong and you are suggesting re-introducing
> > calls to the old API under this #ifdef, is that the case?
>
> Yub. zswap could abstract that part under #ifdef to keep old behavior.
We can reconsider this option when zsmalloc implements reclaim
callback. So far it's obviously too much a mess for a reason so weak.
> >
> > Best regards,
> > Vitaly
> >
> > >
> > > > * @map: map a handle.
> > > > * @unmap: unmap a handle.
> > > > * @total_size: get total size of a pool.
> > > > @@ -100,6 +101,7 @@ struct zpool_driver {
> > > > int (*shrink)(void *pool, unsigned int pages,
> > > > unsigned int *reclaimed);
> > > >
> > > > + bool sleep_mapped;
> > > > void *(*map)(void *pool, unsigned long handle,
> > > > enum zpool_mapmode mm);
> > > > void (*unmap)(void *pool, unsigned long handle);
> > > > @@ -112,5 +114,6 @@ void zpool_register_driver(struct zpool_driver *driver);
> > > > int zpool_unregister_driver(struct zpool_driver *driver);
> > > >
> > > > bool zpool_evictable(struct zpool *pool);
> > > > +bool zpool_can_sleep_mapped(struct zpool *pool);
> > > >
> > > > #endif
> > > > diff --git a/mm/zpool.c b/mm/zpool.c
> > > > index 3744a2d..5ed7120 100644
> > > > --- a/mm/zpool.c
> > > > +++ b/mm/zpool.c
> > > > @@ -23,6 +23,7 @@ struct zpool {
> > > > void *pool;
> > > > const struct zpool_ops *ops;
> > > > bool evictable;
> > > > + bool can_sleep_mapped;
> > > >
> > > > struct list_head list;
> > > > };
> > > > @@ -183,6 +184,7 @@ struct zpool *zpool_create_pool(const char *type, const char *name, gfp_t gfp,
> > > > zpool->pool = driver->create(name, gfp, ops, zpool);
> > > > zpool->ops = ops;
> > > > zpool->evictable = driver->shrink && ops && ops->evict;
> > > > + zpool->can_sleep_mapped = driver->sleep_mapped;
> > > >
> > > > if (!zpool->pool) {
> > > > pr_err("couldn't create %s pool\n", type);
> > > > @@ -393,6 +395,17 @@ bool zpool_evictable(struct zpool *zpool)
> > > > return zpool->evictable;
> > > > }
> > > >
> > > > +/**
> > > > + * zpool_can_sleep_mapped - Test if zpool can sleep when do mapped.
> > > > + * @zpool: The zpool to test
> > > > + *
> > > > + * Returns: true if zpool can sleep; false otherwise.
> > > > + */
> > > > +bool zpool_can_sleep_mapped(struct zpool *zpool)
> > > > +{
> > > > + return zpool->can_sleep_mapped;
> > > > +}
> > > > +
> > > > MODULE_LICENSE("GPL");
> > > > MODULE_AUTHOR("Dan Streetman <ddstreet@xxxxxxxx>");
> > > > MODULE_DESCRIPTION("Common API for compressed memory storage");
> > > > diff --git a/mm/zswap.c b/mm/zswap.c
> > > > index 182f6ad..67d4555 100644
> > > > --- a/mm/zswap.c
> > > > +++ b/mm/zswap.c
> > > > @@ -935,13 +935,20 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
> > > > struct scatterlist input, output;
> > > > struct crypto_acomp_ctx *acomp_ctx;
> > > >
> > > > - u8 *src;
> > > > + u8 *src, *tmp;
> > > > unsigned int dlen;
> > > > int ret;
> > > > struct writeback_control wbc = {
> > > > .sync_mode = WB_SYNC_NONE,
> > > > };
> > > >
> > > > + if (!zpool_can_sleep_mapped(pool)) {
> > > > +
> > > > + tmp = kmalloc(entry->length, GFP_ATOMIC);
> > > > + if (!tmp)
> > > > + return -ENOMEM;
> > > > + }
> > > > +
> > > > /* extract swpentry from data */
> > > > zhdr = zpool_map_handle(pool, handle, ZPOOL_MM_RO);
> > > > swpentry = zhdr->swpentry; /* here */
> > > > @@ -979,6 +986,14 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
> > > > dlen = PAGE_SIZE;
> > > > src = (u8 *)zhdr + sizeof(struct zswap_header);
> > > >
> > > > + if (!zpool_can_sleep_mapped(pool)) {
> > > > +
> > > > + memcpy(tmp, src, entry->length);
> > > > + src = tmp;
> > > > +
> > > > + zpool_unmap_handle(pool, handle);
> > > > + }
> > > > +
> > > > mutex_lock(acomp_ctx->mutex);
> > > > sg_init_one(&input, src, entry->length);
> > > > sg_init_table(&output, 1);
> > > > @@ -1033,7 +1048,11 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
> > > > spin_unlock(&tree->lock);
> > > >
> > > > end:
> > > > - zpool_unmap_handle(pool, handle);
> > > > + if (zpool_can_sleep_mapped(pool))
> > > > + zpool_unmap_handle(pool, handle);
> > > > + else
> > > > + kfree(tmp);
> > > > +
> > > > return ret;
> > > > }
> > > >
> > > > @@ -1235,7 +1254,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> > > > struct zswap_entry *entry;
> > > > struct scatterlist input, output;
> > > > struct crypto_acomp_ctx *acomp_ctx;
> > > > - u8 *src, *dst;
> > > > + u8 *src, *dst, *tmp;
> > > > unsigned int dlen;
> > > > int ret;
> > > >
> > > > @@ -1256,12 +1275,29 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> > > > goto freeentry;
> > > > }
> > > >
> > > > + if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
> > > > +
> > > > + tmp = kmalloc(entry->length, GFP_ATOMIC);
> > > > + if (!tmp) {
> > > > + ret = -ENOMEM;
> > > > + goto freeentry;
> > > > + }
> > > > + }
> > > > +
> > > > /* decompress */
> > > > dlen = PAGE_SIZE;
> > > > src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
> > > > if (zpool_evictable(entry->pool->zpool))
> > > > src += sizeof(struct zswap_header);
> > > >
> > > > + if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
> > > > +
> > > > + memcpy(tmp, src, entry->length);
> > > > + src = tmp;
> > > > +
> > > > + zpool_unmap_handle(entry->pool->zpool, entry->handle);
> > > > + }
> > > > +
> > > > acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> > > > mutex_lock(acomp_ctx->mutex);
> > > > sg_init_one(&input, src, entry->length);
> > > > @@ -1271,7 +1307,11 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> > > > ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
> > > > mutex_unlock(acomp_ctx->mutex);
> > > >
> > > > - zpool_unmap_handle(entry->pool->zpool, entry->handle);
> > > > + if (zpool_can_sleep_mapped(entry->pool->zpool))
> > > > + zpool_unmap_handle(entry->pool->zpool, entry->handle);
> > > > + else
> > > > + kfree(tmp);
> > > > +
> > > > BUG_ON(ret);
> > > >
> > > > freeentry:
> > > > @@ -1279,7 +1319,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> > > > zswap_entry_put(tree, entry);
> > > > spin_unlock(&tree->lock);
> > > >
> > > > - return 0;
> > > > + return ret;
> > > > }
> > > >
> > > > /* frees an entry in zswap */
> > > > --
> > > > 2.7.4
> > > >
> > > >
