> From: Ric Mason [mailto:ric.masonn@xxxxxxxxx] > Subject: Re: [PATCH] staging/zcache: Fix/improve zcache writeback code, tie to a config option > > On 02/07/2013 02:27 AM, Dan Magenheimer wrote: > > It was observed by Andrea Arcangeli in 2011 that zcache can get "full" > > and there must be some way for compressed swap pages to be (uncompressed > > and then) sent through to the backing swap disk. A prototype of this > > functionality, called "unuse", was added in 2012 as part of a major update > > to zcache (aka "zcache2"), but was left unfinished due to the unfortunate > > temporary fork of zcache. > > > > This earlier version of the code had an unresolved memory leak > > and was anyway dependent on not-yet-upstream frontswap and mm changes. > > The code was meanwhile adapted by Seth Jennings for similar > > functionality in zswap (which he calls "flush"). Seth also made some > > clever simplifications which are herein ported back to zcache. As a > > result of those simplifications, the frontswap changes are no longer > > necessary, but a slightly different (and simpler) set of mm changes are > > still required [1]. The memory leak is also fixed. > > > > Due to feedback from akpm in a zswap thread, this functionality in zcache > > has now been renamed from "unuse" to "writeback". > > > > Although this zcache writeback code now works, there are open questions > > as how best to handle the policy that drives it. As a result, this > > patch also ties writeback to a new config option. And, since the > > code still depends on not-yet-upstreamed mm patches, to avoid build > > problems, the config option added by this patch temporarily depends > > on "BROKEN"; this config dependency can be removed in trees that > > contain the necessary mm patches. > > > > [1] https://lkml.org/lkml/2013/1/29/540/ https://lkml.org/lkml/2013/1/29/539/ > > shrink_zcache_memory: > > while(nr_evict-- > 0) { > page = zcache_evict_eph_pageframe(); > if (page == NULL) > break; > zcache_free_page(page); > } > > zcache_evict_eph_pageframe > ->zbud_evict_pageframe_lru > ->zbud_evict_tmem > ->tmem_flush_page > ->zcache_pampd_free > ->zcache_free_page <- zbudpage has already been free here > > If the zcache_free_page called in shrink_zcache_memory can be treated as > a double free? Thanks for the code review and sorry for the delay... zcache_pampd_free() only calls zcache_free_page() if page is non-NULL, but in this code path I think when zcache_pampd_free() calls zbud_free_and_delist(), that function determines that the zbudpage is dying and returns NULL. So unless I am misunderstanding (or misreading the code), there is no double free. Thanks, Dan _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
