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bh=wSRahjjgGZuy7SAGmGAziVDOy+dePLJGxm+nbGz1xQs=; b=aYAGyq/2wqdOkP8YeTLDmFkoGnj7AUK6zmfiEc8ZD3TzuTBVEmYzJEcVPj9RLxWcBRc99E tsAb5P4tyE8k/V+zft986NK3olE+pnkr0qx0FCf2ys5mktD1THwrz7pSNWVlvU3MfSj3eK gFwVx1eDDrUvJELD2VU5BIVhD+C1ZlQ= X-Rspam-User: Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=suse.de header.s=susede2_rsa header.b="0r2him/7"; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b="Jv/sE0gz"; spf=pass (imf20.hostedemail.com: domain of osalvador@suse.de designates 195.135.220.29 as permitted sender) smtp.mailfrom=osalvador@suse.de; dmarc=pass (policy=none) header.from=suse.de X-Rspamd-Server: rspam06 X-Stat-Signature: e9jqtcwzwyriukf9tnb6x7jxthj7fd94 X-Rspamd-Queue-Id: 56C681C0083 X-HE-Tag: 1662436495-263631 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Sep 05, 2022 at 10:57:20PM +0200, Andrey Konovalov wrote: > On Mon, Sep 5, 2022 at 5:10 AM Oscar Salvador wrote: > > +enum stack_depot_action { > > + STACK_DEPOT_ACTION_NONE, > > + STACK_DEPOT_ACTION_COUNT, > > +}; > > Hi Oscar, Hi Andrey > Why do we need these actions? Why not just increment the refcount on > each stack trace save? Let me try to explain it. Back in RFC, there were no actions and the refcount was incremented/decremented in __set_page_ownwer() and __reset_page_owner() functions. This lead to a performance "problem", where you would look for the stack twice, one when save it and one when increment it. We figured we could do better and, at least, for the __set_page_owner() we could look just once for the stacktrace when calling __stack_depot_save, and increment it directly there. We cannot do that for __reset_page_owner(), because the stack we are saving is the freeing stacktrace, and we are not interested in that. That is why __reset_page_owner() does: <--- depot_stack_handle_t alloc_handle; ... alloc_handle = page_owner->handle; handle = save_stack(GFP_NOWAIT | __GFP_NOWARN, STACK_DEPOT_ACTION_NONE); page_owner->free_handle = handle stack_depot_dec_count(alloc_handle); ---> alloc_handle contains the handle for the allocation stacktrace, which was set in __set_page_owner(), and page_owner->free handle contains the handle for the freeing stacktrace. But we are only interested in the allocation stack and we only want to increment/decrement that on allocation/free. > Could you split out the stack depot and the page_owner changes into > separate patches? I could, I am not sure if it would make the review any easier though, as you could not match stackdepot <-> page_owner changes. And we should be adding a bunch of code that would not be used till later on. But I can try it out if there is a strong opinion. thanks for your time! -- Oscar Salvador SUSE Labs