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Tue, 01 Oct 2024 19:12:26 -0700 (PDT) MIME-Version: 1.0 References: <20241002012042.2753174-1-nphamcs@gmail.com> <20241002012042.2753174-2-nphamcs@gmail.com> In-Reply-To: From: Yosry Ahmed Date: Tue, 1 Oct 2024 19:11:49 -0700 Message-ID: Subject: Re: [PATCH v2 1/1] swap: shmem: remove SWAP_MAP_SHMEM To: Nhat Pham Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, hughd@google.com, shakeel.butt@linux.dev, ryan.roberts@arm.com, ying.huang@intel.com, chrisl@kernel.org, david@redhat.com, kasong@tencent.com, willy@infradead.org, viro@zeniv.linux.org.uk, baohua@kernel.org, chengming.zhou@linux.dev, v-songbaohua@oppo.com, linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 8623840017 X-Stat-Signature: sau4fh9tg7rt797hg9f9nk1pwbtpdbjr X-Rspam-User: X-HE-Tag: 1727835148-573408 X-HE-Meta: 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 FBkMrN0N qIQYHr5nPoyZlY0UC+3FLfjtUHPTYnY0w6/gw41IXQWQaU6zfVESua3CCTbjHwtkwJabssWI7sXssketOhbsgXbyh7OHOEATwsfWaTCRorTUd5+5kBsz9BllqqqLBzmrrxX9sNCrO396LpdwMv2EG+P/vtgY/EnqWszgN9r/UhPbNQ32rBNhU1AAjWAV1xDLL/b27SQQxKYMa3BZLvXgmBRS0UX3FYMQIpjlwdNlWalrQUrvhpZlpAamtIA== 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: List-Subscribe: List-Unsubscribe: [..] > > > + * > > > + * @entry: first swap entry from which we want to increase the refcount. > > > + * @nr: Number of entries in range. > > > + * > > > * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required > > > * but could not be atomically allocated. Returns 0, just as if it succeeded, > > > * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which > > > * might occur if a page table entry has got corrupted. > > > + * > > > + * Note that we are currently not handling the case where nr > 1 and we need to > > > + * add swap count continuation. This is OK, because no such user exists - shmem > > > + * is the only user that can pass nr > 1, and it never re-duplicates any swap > > > + * entry it owns. > > > > Do we need this comment when we have the WARN + comment in __swap_duplicate()? > > Here I'm just being cautious and include the limitation of the > function in the API documentation itself. > > No strong opinions though. Maybe it would be more useful to add a warning in the loop if nr > 1, with a comment that explains that the current -ENOMEM handling does not properly handle nr > 1? > > > > > */ > > > -int swap_duplicate(swp_entry_t entry) > > > +int swap_duplicate_nr(swp_entry_t entry, int nr) > > > { > > > int err = 0; > > > > > > - while (!err && __swap_duplicate(entry, 1, 1) == -ENOMEM) > > > + while (!err && __swap_duplicate(entry, 1, nr) == -ENOMEM) > > > err = add_swap_count_continuation(entry, GFP_ATOMIC); > > > return err; > > > } > > > -- > > > 2.43.5