On 2023/12/13 06:58, Nhat Pham wrote:
> On Wed, Dec 6, 2023 at 1:46 AM Chengming Zhou
> <zhouchengming@xxxxxxxxxxxxx> wrote:
>>
>> In the !zpool_can_sleep_mapped() case such as zsmalloc, we need to first
>> copy the entry->handle memory to a temporary memory, which is allocated
>> using kmalloc.
>>
>> Obviously we can reuse the per-compressor dstmem to avoid allocating
>> every time, since it's percpu-compressor and protected in mutex.
>
> Ah this sounds like a good idea. We have to grab that mutex anyway -
> might as well use the memory slot that is protected by that mutex.
>
>>
>> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>> ---
>> mm/zswap.c | 29 +++++++++--------------------
>> 1 file changed, 9 insertions(+), 20 deletions(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index a6b4859a0164..d93a7b58b5af 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -1758,9 +1758,9 @@ bool zswap_load(struct folio *folio)
>> struct zswap_entry *entry;
>> struct scatterlist input, output;
>> struct crypto_acomp_ctx *acomp_ctx;
>> - u8 *src, *dst, *tmp;
>> + unsigned int dlen = PAGE_SIZE;
>> + u8 *src, *dst;
>> struct zpool *zpool;
>> - unsigned int dlen;
>> bool ret;
>>
>> VM_WARN_ON_ONCE(!folio_test_locked(folio));
>> @@ -1782,27 +1782,18 @@ bool zswap_load(struct folio *folio)
>> goto stats;
>> }
>>
>> - zpool = zswap_find_zpool(entry);
>> - if (!zpool_can_sleep_mapped(zpool)) {
>> - tmp = kmalloc(entry->length, GFP_KERNEL);
>> - if (!tmp) {
>> - ret = false;
>> - goto freeentry;
>> - }
>> - }
>> -
>> /* decompress */
>> - dlen = PAGE_SIZE;
>> - src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
>> + acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>> + mutex_lock(acomp_ctx->mutex);
>>
>> + zpool = zswap_find_zpool(entry);
>> + src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
>> if (!zpool_can_sleep_mapped(zpool)) {
>> - memcpy(tmp, src, entry->length);
>> - src = tmp;
>> + memcpy(acomp_ctx->dstmem, src, entry->length);
>> + src = acomp_ctx->dstmem;
>
> We're moving handle (un)mapping and the memory copying inside the
> critical section protected by the mutex. Seems fine to me -
> zswap_store() already did this IIUC.
>
>> zpool_unmap_handle(zpool, entry->handle);
>> }
>>
>> - acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>> - mutex_lock(acomp_ctx->mutex);
>> sg_init_one(&input, src, entry->length);
>> sg_init_table(&output, 1);
>> sg_set_page(&output, page, PAGE_SIZE, 0);
>> @@ -1813,15 +1804,13 @@ bool zswap_load(struct folio *folio)
>>
>> if (zpool_can_sleep_mapped(zpool))
>> zpool_unmap_handle(zpool, entry->handle);
>> - else
>> - kfree(tmp);
>>
>> ret = true;
>> stats:
>> count_vm_event(ZSWPIN);
>> if (entry->objcg)
>> count_objcg_event(entry->objcg, ZSWPIN);
>> -freeentry:
>
> So it reduces the chance of zswap_load() failure due to unable to
> memory allocation failure? Nice!
>
Yes, no need to allocate temporary memory anymore :)
>> +
>> spin_lock(&tree->lock);
>> if (ret && zswap_exclusive_loads_enabled) {
>> zswap_invalidate_entry(tree, entry);
>>
>> --
>> b4 0.10.1
>
> Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
Thanks for review!
